Recently I helped in chat an user with same problem. He have a fresh new updated dapper (Kubuntu Dapper 64 bit) installation with XFX geforce 5700 ultra (driver 8762), 1280 * 1024 resolution. His PC freeze when loggin out. Removing splash solved the issue.
Hope that helps. -- Freeze in Dapper RC when logging out or shutting down https://launchpad.net/bugs/46874 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs