In today's Politico, Carrie Budoff Brown has a very nice review of Obama's trip overseas and the impact it might have. Obama seems to be enjoying a significant bounce in the Gallup tracking poll in the last few days - his lead jumped from two points (45% to 43%) on July 24 to nine points (49% to 40%) as of yesterday.
Clearly, this is - at a minimum - a short-term "good-news" effect. It could also turn out to have long-term positive consequences for Obama as the trip may have addressed voters' questions about his leadership ability. But I still think it's a mistake to attempt to go toe-to-toe with McCain on foreign/defense/security policy.