Crack legal bloggers parse today's historic decision: Glenn Greenwald, argues that the court has also filleted the legal arguments behind the administration's illicit wire-tap shemes:
The Court dealt several substantial blows to the administration's theories of executive power beyond the military commission context. And, at the very least, the Court severely weakened, if not outright precluded, the administration's legal defenses with regard to its violations of FISA.
Marty Lederman is all over the war-crimes angle:
This almost certainly means that the CIA's interrogation regime is unlawful, and indeed, that many techniques the Administation has been using, such as waterboarding and hypothermia (and others) violate the War Crimes Act (because violations of Common Article 3 are deemed war crimes).
If I'm right about this, it's enormously significant.