My prediction - and I made the same prediction for John Kerry if he had won - for President-elect Obama is that for the first year when it comes to domestic squabbles the biggest pain in his butt will be from the left of his own party rather than the right.
The current GOP is a shell of itself, wandering around in the wilderness questioning its core values. In 2000 we Democrats had the advantage of losing on a technicality, and even in 2004 if Ohio had flipped we would have won, but the GOP got their rears handed to them a month ago and are coming off of one of the worst presidents in history.
Democrats on the other hand are at an almost New Deal level of power. Even if Al Franken and Jim Martin fall short (as I suspect), Obama has the capital to bend Republicans to his will on top issues - especially economic ones. But the left flank of the party is already grumbling some on the cabinet appointments, and while it hasn't broken through people who invested more liberalism in Obama than he has are likely to make some noise. Now, if you actually listened to what he said rather than what you want him to say, you would have heard a progressive pragmatist who at the end of the day will have been one of our most progressive presidents - certainly post-Nixon - but is not in the Kucinich/ Nader world (and he wouldn't have had the support of folks like me if he was).
After Clinton won, the left went after him in a way I believe softened him up for the later assault by the right (and the Clintons didn't win any friends by trying to ram things like that version of universal healthcare through). I hope we don't repeat that same mistake, but I'm still expecting those misguided concerns to burrow through anyhow.