The margin, coincident with the extensive U.S. news coverage of Obama's foreign tour, is the largest for Obama over McCain measured since Gallup began tracking the general election horserace in March.
Update: Research 2000 has released a new poll that also shows Obama with a commanding lead when the field includes four candidates:
Psychodrew in the comments points out that Rasmussen says Obama's bounce is fading, but I think it's too early to say what is happening. Generally, in my observation, when different polls begin to give wildly different results, something is happening in the electorate. We need to see where everything lands.