(1) I tend to agree with Another Damned Medievalist in the comments to one of my posts, on the question of "what historians have traditionally supposed they could achieve":
What do you mean by traditionally? Do you mean Herodotus? Thucydides? Tacitus? They all had very different purposes. Gibbon? Carlyle? Also different. Hegel -- still different.
I think this is a fair argument, and quite right (I can't help but smile at the thought of Gibbon and Hegel trying to convince each other on the issue of what the purpose of doing history is); and it's relevant to issues of philosophy of history. I don't think it plays much role in the part of the dispute which interested me most, though (and which I'll get to below).
(2) Just as some of the things said by the philosophers about history have sounded strange to the historians some of the things said by the historians about philosophy of history sound strange to a philosopher's ears. I would tend to defer to the historians on the actual practice of history as a discipline; but philosophy of history as a discipline is necessarily rather more than 'having a philosophy of history' (although obviously there's a connection). This isn't actually surprising; when philosophers do philosophy of history they are not typically doing it merely for the purpose of writing better history (or any history at all), but for what it shows about other things. One of the things that Newall says in his Philosophy of History essay which has received comment is that some have read him as saying that there's something wrong with history; when actually he's simply looking at some philosophical issues raised by the discipline of history and trying to put them in an elementary form (more on this below).
(3) In one of the comments somewhere it was said that the essay read as if there had been no advances in historical scholarship since WWI (or something to that effect); which is possible. Philosophy of history has been a very, very weak field for a long time now, and one of the reasons is that philosophers have, with a handful of relevant exceptions, just largely not tried to set down the issues involved. In other words, the problem is probably rather that the philosophy of history has not kept pace, simply because it hasn't been a particularly thriving field (unlike, say, philosophy of science). (I don't know, of course, what sources influenced Newall's essay.) One of the nice things about this discussion, despite the fact that it has degenerated, is that it provides an opportunity for historians to get out there and show what work needs to be done to bring it up to date. (For why I think this is essential for historians, see (4).)
(4) It is very likely that philosophy of history will contribute very little to the doing of history as such. I make this prognostication on the basis of the fact that philosophy of science has contributed relatively little to the doing of science as such, and philosophy of science is a more developed discipline than philosophy of history. This isn't to say that there won't be any such contributions. The ideal, in fact, would be for philosophy of history to have its equivalent of William Whewell, the great nineteenth-century philosopher of science who was responsible for much of the way science organized itself. But Whewells aren't found on every street corner, so we'll probably have to settle for something less. What philosophy of science has in every generation a massive influence on, however, is what society does with science; and there's no reason to think philosophy of history is any different. A problematic approach to philosophy of science (to the extent it becomes accepted) will distort, at least to some extent, the role science has in society, perhaps even to the extent of eventually distorting the practice of science itself. One of the reasons I think this sort of discussion is a good one to have is that historians cannot afford to ignore philosophy of history because, however historians may view philosophy of history, philosophy of history is what in fact mediates between them and everyone else in society; and it is better that (1) it do so explicitly rather than implicitly, critically examined and out in the open rather than unremarked; and (2) historians be clear about what they see as incorrect (and correct) assumptions in a given sort of approach; and (3) any problems, as far as communicating accurately what they are doing, in the way historians are formulating their approaches and conclusions to the public be corrected as soon as possible; the sort of general epistemological issues discussed in Newall's essay may not seem important for the practice of history itself, but they are essential for making sure that historians aren't going around confusing the bejeepers out of the general public. Even if it weren't important for historians what society does with their results (I have difficulty believing it isn't, but if it weren't), society needs them to take an active concern with the philosophy of history. How else will they judge the good historical work from the bad? (I have nightmares about public problems like that biologists have with evolution springing up in disciplines like history.) So we really do need there to be historians out there clarifying what they are actually doing when they are doing history explicitly in the context of issues raised by the philosophy of history. (In comments to this post, Another Damned Medievalist noted that part of what concerns her is that Cantor's book, "somewhat aimed at a popular audience and definitely read by a popular audience, is somewhat misleading" - which I think captures perfectly, for this particular issue, part of why we need historians interacting with these issues generally.)
(5) Newall, if I understand him a-right, takes what might be called an anti-realist stance on history, and I think this is part of what some have objected to. It's not actually surprising that historians tend to historical realism any more than it is surprising that scientists tend to scientific realism. Now, just as scientific anti-realism isn't the claim that scientists are wrong in their basic practice, I don't think Newall can be interpreted as saying that historians are wrong in their basic practice. I am very sympathetic to an anti-realist position when it comes to history (but then, I am very sympathetic to anti-realist positions when it comes to science) but I think I tend to be realist; in part because I don't, on further thought, think history actually has the verisimilitude problem Newall thinks it does. Underdetermination is not sufficient to create this problem, because underdetermination in itself merely introduces vagueness in what our evidences allow us to conclude as true; even given that underdetermination is pervasive, all this means for the realist is that a lot of times our true conclusions will be vague. And in fact, I think it is necessary to be a realist to allow that the evidences the historian faces are traces of the past. A strict historical anti-representationalism, I think, requires that we cease to treat our evidences as traces of the past, and simply regard our treatment of them as 'traces of the past' as something useful - for what, I'm not sure, since history doesn't have the uses science does; so I'm not even sure we can actually formulate a notion of history at all if we are strictly anti-realist about it.
If we can regard our evidences as traces of the past, their being traces of the past will suffice to allow at least a very basic sort of realism, because it isn't necessary for historians to compare their theories with the actual past, since comparing them with the traces of the past insofar as they are actually remnants of the past will suffice. Again, underdetermination will leave us a bit patchy and vague and with some guesswork; but this falls short of an actual anti-realist position. It is much easier for a historian to be a realist than for some scientists to be so because the historian is to an extent an observationalist; verisimilitude problems no more arise for her than they arise for a scientist whose work consists of observing, classifying, and interrelating the behavior of lions in the Serengetti. There is no sharp distinction in such a case between the correspondence of the theory to reality and its coherence with the evidence; the two generally merge, even if there is some slippage in particular cases. The ethologist has a much, much richer data set to work with; but the historian is, at least in great measure, doing exactly the same sort of thing: there is no sharp distinction between correspondence and coherence for the historian, if (again) we allow that historical evidences are traces of the past. This luxury does not arise for mathematical physics, which is the discipline for which verisimilitude problems most convincingly and acutely arise; but history is not particularly like mathematical physics in the way it poses theories about the world.
Now, I agree with much of what Newall says in the course of arguing for anti-representationalism (and even where I disagree, I find his essay excellent because it does a good job of bringing up the philosophical issues). For instance, I agree that historians should primarily be concerned with the organization of evidences - what we might call the topology of the whole set of historical evidence on the given topic. As I've said before, I think this is almost the whole of what historical scholarship actually is. But insofar as we we can regard these evidences as genuinely historical evidences, there is no problem with being realist. And, while my own historical field, history of philosophy, is about the most historiographically-challenged field of history there could conceivably be (I think the way HoP is taught makes it generally weak on the historical side, although there are particular HoP disciplines which go some way to counteract this, particular for certain lines of scholarship on the medieval and ancient period), I nonetheless find that this fits nicely with my own experience. It's virtually impossible for me not to characterize what I do in realist terms, because what I am doing in describing the whole topology of historical evidences is nothing other than developing a more verisimilar account. My interpretation of Hume's Treatise 1.4.2 is more accurate than anything written 20 years ago, and more accurate still than anything written 50 years ago, and more accurate still than anything written 100 years ago, because in drawing in more of the evidences, and more of their interrelations, I am describing with less distortion and more precision the work Hume actually wrote in the 1730s. This requires, again, that I be able to regard the evidences I actually have on hand (editions of Hume) as genuinely being traces of the past; but the only thing that blocks this is skepticism about the past. And there is no more harm in a historian ignoring skepticism about the past than there is harm in a scientist ignoring external world skepticism. Setting aside skepticism about the past, I actually have, in the archives, the remnants of certain elements of the 1730s themselves, and what I am doing is simply discerning what they are. Because of issues with the evidence (massively organized complexity is the primary one for HoP) it's a trickier business than (say) trying to give the best characterizations of traffic patterns on King Street; but it doesn't, I think, have any more problems with verisimilitude. If a realist historian had a description of a complete set of data, he would have what actually happened in precise detail; that historians always lack a perfectly complete set of data just means that their descriptions can never be perfectly precise and will always have to concede things to ambiguity and vagueness. But this is very different from the verisimilitude problem that arises for the mathematical physicist, because the realist mathematical physicist is theorizing not about the data themselves but about what underlies it, which the data indirectly indicate. Therefore the mathematical physicist does not start off with the very thing he is trying to reach; the historian does, albeit in a patchy and occasionally corrupted form. So no verisimilitude problem arises.
God help me, this post has taken me three hours to write!