I have this same problem, it has just started to happen. only in my case the keyboard goes out as well, so i basically have to resort to hard resetting.
so far i have not found any similarities in instances that it has gone out. one time i was trying to empty my trash, and another i was trying to change a track in the music program Amarok -- gnome locks up, does not respond to kbd or mouse https://bugs.launchpad.net/bugs/109740 You received this bug notification because you are a member of Ubuntu Desktop Bugs, which is a bug contact for meta-gnome2 in ubuntu. -- desktop-bugs mailing list desktop-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/desktop-bugs
