Tom Goldstein at ScotusBlog has an interim report:

Based on the questions posed to Paul Clement, the lead attorney for the state challengers to the individual mandate, it appears that the mandate is in trouble.  It is not clear whether it will be struck down, but the questions that the conservative Justices posed to Clement were not nearly as pressing as the ones they asked to Solicitor General Verrilli.  On top of that, Clement delivered a superb presentation in response to the more liberal Justices’ questions.  Perhaps the most interesting point to emerge so far is that Justice Kennedy’s questions suggest that he believes that the mandate has profound implications for individual liberty: he asked multiple times whether the mandate fundamentally changes the relationship between the government and individuals, so that it must surpass a special burden.  At this point, the best hope for a fifth or sixth vote may be from the Chief Justice or Justice Alito, who asked hard questions to the government, but did not appear to be dismissive of the statute’s constitutionality.

Side note: Paul Clement was the attorney chosen by the House to defend DOMA when the Justice Department reversed its position, resulting in the threats against his law firm King & Spalding, causing Clement to leave the firm.

Lyle Dennison has this (predictable) post-argument assessment, It’s Kennedy’s Call:

If Justice Anthony M. Kennedy can locate a limiting principle in the federal government’s defense of the new individual health insurance mandate, or can think of one on his own, the mandate may well survive.  If he does, he may take Chief Justice John G. Roberts, Jr., along with him.  But if he does not, the mandate is gone.  That is where Tuesday’s argument wound up — with Kennedy, after first displaying a very deep skepticism, leaving the impression that he might yet be the mandate’s savior.

If the vote had been taken after Solicitor General Donald B. Verrilli, Jr., stepped back from the lectern after the first 56 minutes, and the audience took a mid-argument stretch, the chances were that the most significant feature of the Affordable Care Act would have perished in Kennedy’s concern that it just might alter the fundamental relationship between the American people and their government.   But after two arguments by lawyers for the challengers — forceful and creative though they were — at least doubt had set in. and expecting the demise of the mandate seemed decidedly premature.

Update:  Transcript, Audio.