On August 14, Nate Silver put together a projection of what the polling would look like after both conventions had passed.
All I can say is the guy is a total freak, because he pretty much nailed it: as of right now, we're basically exactly where he predicted that we would be -- John McCain, with a small lead.
Here's a chart showing Nate's projection:

The value of this chart is that it demonstrates that these shifts in opinion were entirely predictable.
Going forward, there may be a slow drift in the next few weeks, but the next big shift won't take place until the first presidential debate on Friday September 26.
At this point, what matters most is the fundamental question of the campaign, and now that both sides agree that this is a change election, I'd still rather be in our position than their's.
© Jed Lewison