As noted in the quick hit by Kal, the most recent Gallup tracking has Obama up 6, up from a tied race a week ago. This puts Obama's bounce at 6, or just above the post '92 average of 5.7 points. Importantly, though, this is BEFORE Obama has given his acceptance speech, and only partially reflects the impact of what was a brilliant night last night. Ramsussen also has noted the beginning of an Obama bounce, though it appears to be smaller in their polling.
On Tuesday I wrote that I thought the election might be decided by the speeches the Clintons would give. As of this writing, there is solid evidence to suggest that their performance has given Obama a significant lead. It is worth noting that at no point during the 2004 Convention did Kerry show anything similar to the bounce that Obama has already received.
Typically Convention bounces tend to fade after a couple of weeks. This means that typically the second convention's narrative is only partially effected by the success of the first. There is no time this year, however, for the bounce to fade. The opportunity exists, therefore, that the GOP Convention will be held within the context of a growing Obama lead. But their convention lacks the dramatic elements that the Democratic Convention possesed. As a result, it appears increasingly likely to me that Obama will carry a lead into September.