I did a long write-up on the debate over at Plum Line, so I'll mostly just send you there. If you missed it, but enjoy presidential debates in general, I'll recommend this one: started with a bang, and rarely let up.
As I said over there, how it will affect GOP voters in the short run depends mostly on what spin is accepted within the GOP partisan press; there's certainly plenty of great clips to support virtually any interpretation. Beyond that, I'm very curious about how Rick Santorum's attacks, especially his quite vicious and personal attacks on Newt, played to conservative audiences. It played really well to me, and in my view any conservative should buy the idea that Newt absolutely cannot be trusted, but I'll certainly confess that I'm not exactly neutral on that subject.
And I'll also repeat what I said over there about John King: he totally, totally screwed up the "open marriage" question. Probably his best bet was to just leave it alone, but if he really wanted to press it he could have framed it better in lots of different ways. All that said: don't assume that five good minutes from Newt makes the issue go away. Among other things, Jay Leno and the rest of that gang aren't going to lay off just because a partisan crowd fell for a cheap rhetorical trick. Don't forget, too, that his marriage record is only one of Newt's many, many, many vulnerabilities. I wouldn't want to guess how it affects him in South Carolina in the short term, but in the long term very few Republican politicians or operatives really want to spend all summer and fall defending Newt's personal life.