The complementarian/egalitarian dispute does not really interest me; I think both sides tend to misread the relevant texts and usually miss the whole point, which in every relevant passage is that Christians are not to act in worldly ways like the nations but to show forth the love of Christ. But this question of functional subordination does interest me. With some exceptions that can be set aside here, everyone in the dispute wants to avoid the heresy of subordinationism, which is the claim that Son and Spirit are not equal to the Father but subordinate to him. Now, orthodox Calvinists who accept the functional subordination account, like Jeremy and Rebecca, want to deny subordinationism, but hold that this denial is consistent with a subordination of roles. I agree that most people who hold functional subordination accounts deny subordinationism. I tend to think of functional subordinationists as in some ways parallel to Miaphysites: Miaphysitism is a vague set of claims that can be taken in ways that are Monophysite (and thus heretical) or that are consistent with, albeit unclearly so, with Chalcedonianism (orthodoxy). Likewise, I don't think people like Jeremy and Rebecca have slipped into heresy. I do think that they have slipped into an unedifying discourse that tends in a heretical direction, although they clearly take it in an orthodox way. Functional subordinationism is a set of vague claims that can be taken as Arian (and thus heretical) or as a misleading way of being Cappadocian (and thus orthodox).
In other words, it's an unfortunately confused way of saying things that can be better said in other ways. I think part of the confusion is that functional subordinationism is clearly an inconsistent terminology. Functional subordinationists like to say that the roles of Father, Son, and Spirit are just different, the one not being superior or inferior to the other. Then, however, they say that the Father has a role of authority over Son and Holy Spirit; a relation of authority, however, is a paradigmatic instance of superiority over another.
Further, functional subordinationists like to claim that their position is just traditional orthodoxy. However, it's not as obvious as they usually claim. Traditional orthodoxy is not put in terms of roles. And traditional orthodoxy eschews claims of subordination like the plague. The Father isn't said to have a role of authority over the Son and the Holy Spirit; he is said to be the Principle or Origin of the Godhead. This is an authority-neutral term; the Church Fathers are very explicit about that. Every person of the Trinity has every God-befitting dignity in common -- they share one will, one intellect, one goodness, etc. -- with the only distinction being that the Father possesses it as beign without Principle; the Son possesses it as being from the Principle; and the Spirit possesses it as being from the Principle with the Son. Basil, in his classic work on the Holy Spirit, is very clear that this relation involves no subordination, subnumeration, or any other 'sub'; the Persons of the Trinity are ordinate to each other, not subordinate to each other. It is legitimate to call the Father the First Person of the Trinity only if you do not mean by this that the Father is superior to the others in any way. The only sense in which the Father is First is that He is the Principle of the Godhead. In every other aspect, the Persons are equal, because they share all God-befitting dignities as one. And authority is very clearly a God-befitting dignity.
Sometimes functional subordinationists make it sound as if this were all that were meant. If this were all that were meant, there would be no need to talk about functional subordination: the doctrine is called the monarchy, where 'monarchy' doesn't mean monarchy in our sense but 'single-principle-ness'. But this does not seem to be the point of the functional subordination account.
Jeremy argues in his post that the opponents of the functional subordination account are confusing the economic and the ontological Trinity -- i.e., the Trinity as it is in itself, and the Trinity as manifested in the economy of salvation. He refers readers to a Wikipedia article on it. Unfortunately the article seems confused. For instance, it says:
Economical subordination is implied by the genitive of terms like "Father of", "Son of", and "Spirit of". While orthodox trinitarianism rejects ontological subordination, it affirms that the Father, being the source of all that is, created and uncreated, has a monarchical relation to the Son and the Spirit. Or, in other terms, it is from the Father that the mission of the Breath and Word originate: whatever God does, it is the Father that does it, and always through the Son, by the Spirit. The Father is seen as the "source" or "fountainhead" from which the Son is born and the Spirit proceeds, much as one might observe water bubbling out of a spring without worrying about when it began doing so. However, this language is hemmed in with qualifications so severe that the analogy in view is easily lost, and is a source of perpetual controversy.
The problem with this is that there are not only qualifications of the claim that 'subordination is implied by the genitive of terms like 'Father of', etc.', but Basil and the other Cappadocians seem very clearly to deny it. Basil, for instance, seems to go so far as to say that this whole type of argument is heathen and unbefitting those who take Scripture seriously; and I do not think he is alone in this view. 'Father', 'Son', and 'Spirit', whether with a genitive or not, do not ever imply subordination of any kind, but only equality by relation to the Principle.
The Wikipedia article, however, does make the right distinction between ontological and economic Trinity later. The ontological Trinity is the Trinity understood entirely in its eternal intrapersonal relations. The economic Trinity is the ontological Trinity as manifested in the dispensations of providence: creation, redemption, glorification. The Church Fathers are very clear that the ontological Trinity involves no subordination at all; they are also very clear (pace the article and many functional subordinationists) that the names 'Father', 'Son', and 'Holy Spirit' in themselves describe the relations of the ontological Trinity, which is the Trinity as eternal. The Eternal Trinity involves no subordination at all.
Now, the general background of the economic Trinity is ruled by three basic points that are important to Christian doctrine.
(1) Every operation or act of the Trinity toward creation is a unitary operation shared by Father, Son, and Holy Spirit. It's not the Father alone who creates; when God creates, every person of the Trinity shares the one act of creation.
(2) But they share it as distinct Persons. For instance, this one act of creation is possessed by the Father as being the Origin; it is possessed by the Son as being of the Father; and it is possessed by the Spirit as being of the Father through the Son. If by 'different roles' one means this, then it is perfectly true that orthodox Trinitarianism holds that the Trinity are equal but have different roles. It's just that the roles are not divided up by operation -- the Father doesn't do one thing and the Son another -- but by Person -- every single operation is a unified expression of the role of the Father, the role of the Son, and the role of the Spirit. This is the Cappadocian point that the roles, if you wish to call them that, can be distinguished but not pried apart. The Persons act in an ordered way; but, because their acts are all perfectly unified, there is no room for subordination because the acts are one and the same, as are the goals, and among the persons there is order, not subordination.
(3) However, one of the things God wills is that God be manifested as a Trinity in the scheme of salvation. Thus, although every part of the scheme of the salvation is willed by one indissolubly unified will by the Persons together, what is willed -- the scheme of salvation -- is that the Word (the Son) be made flesh for our sins, and that the Spirit be our Comforter sent from the Son, and that the Son and the Spirit both be sent from the Father. (Thus manifesting the Trinity in the divine works.) At this point subordination does enter in, and if you look at the more plausible functional subordinationist arguments (you can see a number of them in Rebecca's posts), you can see why I'm inclined to say that at least some functional subordinationists, although confused, are entirely orthodox. For if by 'functional subordination' you mean that Christ is subordinate to the Father, you are right. The reason, however, is not that He is subordinate in His eternal role, but that He took the form of a servant -- He made Himself subordinate by becoming an inferior to the Father (namely, a human being). Insofar as He has the form of a servant, human nature, He is subordinate to the Father not merely functionally but naturally. Of course, He is functionally subordinate, too; but He is functionally subordinate because He is naturally subordinate as man.
This is where I think the attempt to use functional subordination in the economic Trinity as an anlogy for the complementarian (at least the one who wants to say that A can be subordinate to B even though A and B are equal) fails utterly. Because the whole point of the analogy was supposed to be that you can have subordination without inequality; but the functional subordination in the economy is a subordination that is created by kenosis (to use Paul's term), a deliberate assuming of inequality for a certain purpose. Nothing in the complementarian position requires that the analogy to the Trinity hold; the only purpose of the analogy is for the subordinationist-complementarian to show that there is an agreed-upon case in which you get something like what the subordinationist-complementarian wants. You can be a complementarian without accepting the notion of functional subordination -- such a complementarian would just hold that men and women have some different significant roles, but not hold that any of these roles are in any proper sense subordinate. (Most people who call themselves complementarians, however, are subordinationist-complementarians.) And you can be a subordinationist-complementarian, i.e., a complementarian who accepts the notion of functional subordination, without holding that the Trinity is a good example of purely functional subordination. But the position that the Trinity is a good example of purely functional subordination seems untenable: As Incarnate, the Son is subordinate because He is inferior -- anything of flesh is inferior to Godhead. (Of course, this is only half the doctrine, since we are all Chalcedonians here; but it is a genuine half of the doctrine.)
So if, like Jeremy and Rebecca, the functional subordinationists hold that the functional subordination is one of the economic Trinity, I think they are orthodox; but I think they are orthodox in a confused [or perhaps it would be better to say 'confusing'--ed.] way. In particularly, they are overlooking the fact that the economic Trinity has equality of Persons, but, due to the human nature of Christ, one inequality of natures. And this is why more traditional orthodox are completely thrown off by their manner of talking. Because it is true that Christ is subordinate to the Father; but this subordination is not something found in the eternal intra-personal relations of the Trinity, as they seem to imply, but is due to the Incarnation, which introduces a complication they seem to be glossing over.