Bill Vallicella at the Maverick Philosopher has a nice post on negative existentials, which is exactly right, I think. I find it interesting, because I've been doing some thinking, off and on, about Meinong and possibilist realism. I don't think Meinongianism is ultimately tenable, but I think it has an undeserved reputation from people who haven't bothered to think it through. For the Meinongian solution to negative existentials -- i.e., that there are nonexistent objects independent of thought -- is a very elegant one. It's usually accused of 'ontological extravagance', but I don't think most people have much of an idea what they mean by phrases like that. There is a straightforward sense in which the Meinongian solution is one of the simplest and most elegant solutions to the problem: it allows you to treat everything you can think about in much the same way. It also allows you to take statements such as "Frictionless planes do not exist" at face value by taking them to be statements about the objects frictionless planes; etc. Likewise, it's often said that there is something weird about saying "There are nonexistent objects," since 'there are' (or existential quantification) implies actual existence; but this is actually not plausible, since existential quantification can apply to fictional entities, instrumental posits, idealizations, etc. -- in short, many things that don't actually exist -- and it is almost impossible to avoid applying it in this way. The Meinongian is not actually proposing something strange in suggesting that nonexistent objects subsist even though they do not exist; or, at least, there is nothing strange about the bare fact that he proposes it, whatever difficulties there may be in being clear about what subsistence is. The ability to talk about modal truths without appeal to the very roundabout and complicated appartus of possible worlds is a potential advantage as well. In other words, the common tendency (among philosophers like myself who haven't studied the matter closely) to dismiss Meinongianism as an obvious absurdity is itself problematic; it seems usually to be based more on a sense of disquiet than on any serious reasons. (Vallicella has pointed out elsewhere that one serious reason to doubt Meinongianism is that it seems to mess up the Cartesian cogito: if Meinong is right, it is possible that I think but do not exist. He also presents an interesting Roycean argument that love and self-love give us another serious reason to reject Meinong's claim, which is well worth reading.)
For my part, I incline toward Buridan's position (see Gyula Klima's excellent paper, Quine, Wyman, and Buridan: Three Approaches to Ontological Commitment (PDF)).
UPDATE: Vallicella notices a point on which I didn't get Meinong quite right (the existence/subsistence distinction) -- always a danger for someone who has only done some light reading in a given philosopher. Conventional wisdom always wriggles into the interpretation; and in interpreting philosophical works it's astounding how often conventional wisdom is wrong.
