I'm running 10.1.
10.0.x was unable to cope with 720p YouTube reliably. It dropped a lot of frames.
10.1 copes with 720p YouTube just fine. It can cope with 1080p reasonably well, though incredibly complex scenes (think a rotating checkerboard with 20-50x the normal density of squares) will cause it to drop frames. However for most situations it seems to cope at full screen (1920x1200). This is on a 2.66, so I expect my frame rates are ~10% better than the 2.4GHz.
I've not yet tried the Gala 2 preview even though the 320M would be hardware accelerated.