Having a similar problem with Kubuntu: complete freeze-up and lack of response to mouse. Sometimes the keyboard still works and sometimes it doesn't. Doesn't seem to be a memory leak (looking at top doesn't reveal anything unsual). Only way to fix it seems to be to restart X and log back in.
-- Xorg process freezes, uses 100% of CPU. Can be killed by remote terminal. https://launchpad.net/bugs/51991 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs