After it became clear that Obama's trip through the Middle East was not only error-free but wildly successful (because of Maliki's gambit), there's been a third wave of press chatter and fretting to the effect that Obama's trip may now be too
successful, that voters on the home front would rather have him stateside addressing their concerns than being feted by adoring Europeans. Joe Klein actually had a good post
on this at Swampland yesterday. In the short term sense, I don't think watching Obama walk on water in Europe (or in whatever lakes or rivers they have available) will goose his poll numbers. It may even have a bit of the reverse effect. The key was banking a solid trip abroad, an audition for the head of state/commander-in-chief role, that he'll be able to refer back to (mostly implicitly, sometimes explicitly) during the tough weeks ahead in the fall.
So I don't think anyone should be surprised that his numbers aren't spiked. The reverse might even happen. But it's still a key step since fundamentally this election is about hiring Obama, and overcoming the residual doubts (about his newness, youth, funny name, whatever) that are allowing John McCain even to stay in contention.
It's not Obama v. McCain. This is about Obama, with McCain as the alternative.