For whatever it's limited worth, I thought McCain had a few opportunities to do some real damage tonight, and basically blew it. For example, on the Ayers issue, if McCain was going to use it at all, once Obama acknowledged that he and Ayers served on a foundation board together, McCain could have come back with Obama's quote from his debate with Hilary, in which he suggested that Ayers was just some guy who lived in the neighborhood, and only then added that Obama had either his first, or one of his first, fundraising get-togethers in Ayers' home. That would have reinforced McCain's point about the issue being Obama's forthrightness with the American people.
When McCain challenged Obama on whether he has ever gone against the party leadership, he could have followed up by pointing out Obama's 100% liberal voting record in the Senate. (Surprising that the "L" word hasn't come up in this campaign, given that the percentage of American's calling themselves liberals is still rather low.)
When Obama discussed his very limited relationship with ACORN, McCain could have noted that it's been well-documented from ACORN's own contemporaneous web publications that Obama worked closely with ACORN over the years--again, hammering on "forthrightness."
When Obama defended increasing taxes by referring to Warren Buffet, McCain could have pointed out that Buffet's income is almost all from capital gains, and that Buffet started out with inherited wealth. By contrast, many entrepreneurs who work their way up from nothing will face marginal state and federal tax rates of almost 60%. McCain could have then challenged Obama to defend the proposition that someone who works 80 hours a week, creating jobs for the community should "spread the wealth" to that extent--my recollection from polls I've seen is that only a tiny fraction of Americans think taxes should be that high for anyone. I can think of a few more examples, but you get the idea.
On the other hand, I thought McCain was effective when he pointed out that he isn't President Bush, and when he called Obama "Senator Government," even if that was inadvertent. But, in general, McCain just isn't able to rattle off the kind of detailed critique that could throw Obama off his game, while Obama plays an excellent defense.
UPDATE: Jennifer Rubin has a similar, but more detailed, analysis.
FURTHER UPDATE: Here are Obama's exact words about ACORN, from the debate transcript: "The only involvement I've had with ACORN was I represented them alongside the U.S. Justice Department in making Illinois implement a motor voter law that helped people get register (sic) at DMVs." It's all over the blogs, with links to sources, that Obama was a trainer for ACORN. The Obama campaign itself changed its "Fight the Smears" website from stating "Fact: Barack was never an ACORN trainer and never worked for ACORN in any other capacity," to "Fact: ACORN never hired Obama as a trainer, organizer, or any type of employee." That's an implicit acknowledgment that Obama worked for/with, but was never officially "hired" by, ACORN. It was a pretty brazen, and seemingly unnecessary, lie by Obama, but McCain didn't call him on it.
And how about this for the relevance to McCain's campaign: "We are going through a terrible economic crisis that few Americans understand. American will have to trust their leaders when we propose solutions to this crisis. We are still engaged in a 'War on Terror' that necessarily involves secret intelligence work and covert action, and that requires the American people to trust their president. If Barack Obama can't be forthright about [Ayers, ACORN, his position on gun control pre-2008, and so on], how can Americans trust him on the economic crisis and issues of life and death."
Note that I don't think that Obama is necessarily less trustworthy than McCain, and I, in fact, don't trust either of them, or any "political leader." McCain, however, does have the advantage of having a (perhaps undeserved) reputation for straight talk, while Obama has a Clintonian lawyerly way of evading difficult questions, and, for that matter, he also tends to pass the buck to subordinates when people point out that he took some rather non-mainstream positions in his legislative campaigns. If McCain were a more effective campaigner, he could be taking better advantage of this dynamic.