So the driver seems to have improved a lot - I can finally watch videos smoothly in fullscreen. Although performance isn't quite what it could be. Running glxgears with compiz runs at ~490 fps. Sort of to be expected, because compiz isn't exactly meant to be run with anything graphically intensive.
But aside from that, moving any windows with a video running makes that video become very choppy and unwatchable. Basically every window that is partially not shown but moved into view slows performance down severely.
Anyone else have this problem? Any fixes? By the way, aside from the driver and installing restricted codecs, I have a totally unmodified install of Ubuntu (aside from updates).