My gut feeling is that that lap was a "Hamilton special" and that he wont be able to consistently grind out that sort of lap time.
Although the BrawnGP cars havent done anything amazing this weekend, I still feel their race pace is going to be very very fast. I honestly cant see how any car can beat a BrawnGP car, unless it rains. Obviously if Button gets stuck behind a slower car (Trulli, for example) and loses 1s/lap to the leader, then this will hurt his chances for the win, but if he doesnt get bogged down in traffic, I can see him with a very good chance of a win.
Vettel/RedBull's performance is a lot better than I would've expected, so obviously, he and his team will fancy their chances for a win tomorrow. If it rains, then obviously Vettel has to be favourite, as I feel Hamilton isnt yet ready to compete against for wins yet, in the McLaren while the rest of the people around him on the grid, aren't in Vettel's class when it comes to wet-weather driving.