I only got to watch bits and pieces of the health care summit at Blair House today. From what I saw, and what I've heard and read from others, there wasn't much in the way of real news generated, and certainly wasn't anything that might be considered a "game-changing" moment. Bear in mind that the summit took place on a weekday afternoon, had to compete with the Winter Olympics, and was cut away from (or talked over) at various points by several of the cable networks. The home audience had to be fairly minuscule, so the threshold for a breakthrough moment would have been high.
From what I did see, both the President and the Congressional Democrats certainly had their strong moments -- higher highs than the Republicans -- and I suspect that a high-information voter who watched substantial parts of the debate would come away with a slightly more sympathetic view of their position. But (i) there aren't very many high-information voters, and (ii) most of them will have had something better to do than to watch the health care summit. A medium-information voter is more likely to have noticed the testy exchange between President Obama and Senator McCain, which didn't make either of them look particularly good. On the other hand, perhaps the real audience was not so much the voters at home but the D.C. press corps. It's hard to say if either side might make a more tangible gain there as the post-game spin war has yet to really begin.
Fundamentally, one's impression of where the health care debate stands is liable to be very similar to where it was 24 hours ago. Personally, I err a bit on the pessimistic side because (i) the math in the House, already challenging to the Democrats, has gotten even tougher with the death of John Murtha and the impending retirement of Neil Abercrombie; and (ii) it seems like there are a lot of ways the Democrats could fumble the exchange between the bipartisan tone they sought to strike today and their need to pass their policy in a reconciliation/majority-rules environment later on.