The argument in Hamdan.

SCOTUSblog describes today's oral argument in the Hamdan case:

For the most part, the session was subdued and understated, especially given the historic dimensions of the dispute before the Court -- a major test of Executive power in the midst of vigorous presidential responses to a proclaimed "war on terrorism." But there was definitely an emotional high point, and that came when Breyer, then Souter, focused on the law that Congress passed late last year that threatened to scuttle the Hamdan case, and all other pending court cases filed by foreign nationals now being detained at Guantanamo Bay, Cuba. That law, the Detainee Treatment Act, is a court-stripping measure that raises serious questions about whether President Bush's orders dealing with captured foreign detainees will ever be fully tested in court.

Much more at the link.

Here's Gina Holland's description of the argument (for AP):

Justice Anthony M. Kennedy questioned Solicitor General Paul Clement about the legal safeguards for the trials. Justice Stephen Breyer also asked what would stop the president from holding the same type of trial in Toledo, Ohio, not just at the military prison in Guantanamo Bay, Cuba.

Hamdan claims the military commissions established by the Pentagon on Bush's orders are flawed because they violate basic military justice protections.

"This is a military commission that is literally unburdened by the laws, Constitution and treaties of the United States," [Hamdan's lawyer, Neal] Katyal told justices.

UPDATE: Here's Linda Greenhouse:

Justice Souter interrupted [Solicitor General Paul Clement]. "Isn't there a pretty good argument that suspension of the writ of habeas corpus is just about the most stupendously significant act that the Congress of the United States can take," he asked, "and therefore we ought to be at least a little slow to accept your argument that it can be done from pure inadvertence?"

When Mr. Clement began to answer, Justice Souter persisted: "You are leaving us with the position of the United States that the Congress may validly suspend it inadvertently. Is that really your position?"

The solicitor general replied: "I think at least if you're talking about the extension of the writ to enemy combatants held outside the territory of the United States —"

"Now wait a minute!" Justice Souter interrupted, waving a finger. "The writ is the writ. There are not two writs of habeas corpus, for some case and for other cases. The rights that may be asserted, the rights that may be vindicated, will vary with the circumstances, but jurisdiction over habeas corpus is jurisdiction over habeas corpus."