Pat Buchanan made an interesting point on MSNBC just now: While Edwards's endorsement does ease the sting of last night's West Virginia battering, it probably raises expectations for Obama in Kentucky next week.
It's not like he has to win Kentucky. But, with Edwards at his side, the media probably expects him to get a lot closer than 40 points (last night's deficit)--probably a lot closer than 20. Which is a little tricky, since I don't think Edwards is going to help him that much.
For what it's worth, the few polls out there show Hillary up 25-30 points.