had the same problem, X crashed/restarted during high disk IO, copying to USB flash + USB hd. After restart cpu 100%, reading comment above i found 2 x metacity and killed one. That fixed it for me.
$ ps ax | grep meta 6494 ? RN 112:55 /usr/bin/metacity --replace 17758 ? S 0:01 /usr/bin/metacity --replace $ kill -quit 6494 -- metacity process uses 100% CPU https://bugs.launchpad.net/bugs/350174 You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs