I've been running XBMC in Ubuntu 12.04 (64) with Unity for months and never had a problem.

In the last two or three days I've found XBMC's GUI start to become slow and unresponsive and HD playback has become stuttery.

Turning off Vertical Blank Sync within XBMC's settings fixes the GUI lag but not HD playback.

Has anyone else experienced this problem? I'm trying to work out which updates have caused it, I see nvidia-common, jockey-common and xdiagnose were all updated this week, is one of these to blame?