Here is my last minute prediction on the first Obama-Romney debate:
I think Mitt Romney is going to win it. This has nothing to do with the forensic skills of either Romney or Obama, and everything to do with the media.
Historically speaking, they tend to try to make political stories as "exciting" as possible, and as such, usually tend to award "victory" to whichever participant in a debate was perceived as the "underdog" going into it. For example, Ronald Reagan was widely viewed as an intellectual lightweight before his debate with Jimmy Carter in 1980, so the fact that he came across as reasonably articulate and well-informed was perceived as a triumph (his "There you go again" line and query about "Are you better off now than you were four years ago?" reinforced that). Similarly, everyone thought George W. Bush couldn't string two words together in 2000, so the fact that he actually didn't flub anything when he went against Al Gore helped him enormously (Gore exacerbated his problems by coming off as condescending).
There is an exception to that rule, however. Well, a caveat, to be more precise. The candidate has to be competent.
If he makes a fool of himself in some egregious and undeniable way, the media will spin that as the story of the underdog who - instead of coming out ahead - wound up just proving everyone right. Gerald Ford did that in 1976 when he reinforced notions about him being an intellectual lightweight by insisting Eastern Europe wasn't being controlled by the Soviet Union. Similarly, George H. W. Bush did it in 1992 by glancing at his watch during the debate (everyone viewed him as being aloof and not wanting to engage with people, which was consistent with his image at the time). In short, Romney CAN lose tonight, but only if he egregiously screws up. Mere competence or better will probably wind up being depicted as a win for him.
One last bit of news going in: As Nate Silver from FiveThirtyEight.com pointed out today, "although there has been a tendency for the challenging candidate to gain ground immediately after the first debate, there has not been any tendency for the challenger to gain over the remaining weeks of the election."
In short, this is Romney's last chance to remain competitive. The good news for conservatives is that it's likely he'll be able to do so (Silver is skeptical of this, given that no challenger has overcome a deficit as significant as the one currently separating Romney from Obama, but the polls have been so close for most of this election that I don't think Obama's lead is as rigid as those of previous incumbents). The good news for liberals is that if he doesn't - if he makes any major gaffes at all - the odds are very slim that he'll get another chance to repair things. Barring some major calamity for Obama within the next month (and a videotape unearthed by right-wing hit men showing a speech he delivered before his presidency - and which was already covered by the media during his first election - doesn't count, history makes it extremely unlikely he'll be able to win. In short, this debate is do-or-die for him.