More info: It turned out to be a Beryl or Nvidia bug for me. Switching to metacity before switching to another user prevents the hang-up.
Were/are you using Beryl as well Malius? -- Switch user crashes system. https://launchpad.net/bugs/76902 -- desktop-bugs mailing list desktop-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/desktop-bugs
