The Volokh Conspiracy is blogging heavily on this issue. Eugene Volokh is a law prof. at UCLA and very sharp. Here is the crux of his argument (just the high points, it's really long, but worthwhile -- just go to the Conspiracy):
Detainees and unlawful combatants vs. POWs: . . . I've blogged about this general question before, but it seems worth mentioning again; so here are a few thoughts.
1. There's nothing at all novel about the concept of an enemy detainee who isn't a POW. To the best of my knowledge, the practice of civilized nations has long recognized that there are two categories of wartime military captives. The first involves (more or less) soldiers who were fighting in uniform within organized command structures; these are generally seen as being entitled to "prisoner of war" status, which means (a) humane treatment, (b) limits on certain kinds of interrogations, and (c) immunity from being tried for actions that consist of "lawful warfare," e.g., shooting at our soldiers (while fighting in uniform within organized command structures). . .
The second category . . . is that of unlawful combatants. The quintessential examples are spies and saboteurs, but more generally it also includes soldiers who do not fight in uniform within organized command structures. Unlawful combatants are generally not protected in the ways I describe above; they have many fewer rights (I speak here of rights under international conventions and conventional practice) than lawful POWs. In particular, unlawful combatants may be tried and often executed for their unlawful conduct; they don't have the "lawful combatant" immunity from murder laws, for example.
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2. This also suggests, I think, that it doesn't make much sense for purposes of American constitutional law, or the American law of habeas corpus, to provide habeas to unlawful combatants but not to POWs. The distinction is a matter of miiltary practice and treaty law, not of U.S. constitutional law. What's more, it doesn't make a huge deal of sense. Unlawful combatants and POWs are both deprived of their liberty by U.S. forces. Both can claim that they really weren't enemy soldiers, but were caught by mistake. If anything, the detainees who are detained on the grounds that they are thought to be unlawful combatants are likely to be more dangeorus than the POWs.
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3. Now there is of course one important potential difference, which I alluded to in the first item. Once an unlawful combatant is tried and convicted for his unlawful actions, then he does stand in a different position from the POWs: He's not just being detained as a prophylactic measure for the duration of hostilities (however long that might take), but he's being imprisoned for a longer time as a punishment, or even being executed. At that point, there's a more credible case for civilian court review. I think it's probably still pretty weak, for various reasons. But he can no longer be squarely analogized to the bulk of other detainees.
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The current litigation thus isn't challenging punitive detention or execution, which hasn't taken place. Rather, it's challenging prophylactic detention -- the very sort of thing that was indeed done to German and Japanese soldiers captured during World War II.
I'm just worried that the internationalist Justices on the Supreme Court will find some new justification to reconfigure the laws of warfare.