The media is mostly talking about the potential swing votes arguing strongly against the mandate, with a weak defense from the Solicitor General, but I think they're missing the biggest part of this. Listen to Roberts, Alito, and especially Scalia's questions to Verrelli immediately before he switched off to Clement. Here's the biggest exchange:
Scalia: "So you're telling me all the discussion we had earlier about how this is a big uniform scheme and the Commerce Clause, blah blah blah blah, really doesn't matter. This is a tax, and the Federal government could simply have said without all the rest of this legislation, could simply have said, 'Everybody who doesn't buy health insurance at a certain age will be taxed so much money.' Right?"
Solicitor General: "It, ah, it used its powers together, to solve the problem of the market not providing affordable covera--"
Scalia: "Yeah, but you didn't need that, you didn't need that. If it's a tax, raising money is enough."
Solicitor General: "It, it is justifiable under its tax power."
Scalia: "Okay... extraordinary."
Dammit. They're going to be ruling that the Anti-Injunction Act prevents them from deciding the merits of the case, aren't they?