This is pretty cool. If you could figure out some nice CSS3 transition effects for the application of a patch diff it would be even cooler. Like lines sliding and other lines moving down. Maybe with a little bubble up that fades in the Gravatar of the person that made the commit as those lines appear or disappear.

This might be more than just a nice to have. Our eyes are a lot better at detecting small motions than they are small differences. So if you are looking at a big file and keep going through the playback like this, a small change at the bottom that might have missed your attention before will now be very obvious.