Despite ARG's horrid reputation I think this may be fairly accurate. People tend to forget that Delaware has a sizeable black population so its not surprising this one is very close. Plus, Obama has been gaining in national polls of late and this generally reflects that.
Actually, I think Delaware should end up pretty solidly for Obama, if for no other reason than that Obama is the first serious candidate in probably decades to visit the state (in some capacity other than traveling between Maryland and Pennsylvania or New Jersey).
He better win Delaware in a landslide. If I was one of his advisors, I would have had him in New Jersey or Connecticut, state's where more than 5 or so delegates are up for grabs (I know that Delaware has 15 delegates, but with proportionality, there's very little chance that any of the candidates will win less than 5 or 6 delegates).