Comment 27 for bug 560082

Moving .config didn't help, but moving .compiz did, imported compiz backup .profile, done.
$ ps aux | grep compiz
1000 5641 3.1 5.1 344704 52872 ? S 11:27 6:18 compiz
1000 5685 0.0 0.0 4096 576 ? Ss 11:27 0:00 /bin/sh -c /usr/bin/compiz-decorator
1000 10895 0.0 0.0 7636 1008 pts/0 S+ 14:51 0:00 grep --color=auto compiz
$ ps aux | grep metacity
1000 10903 0.0 0.0 7632 920 pts/0 S+ 14:51 0:00 grep --color=auto metacity

Just for the record when no windowmanager is loaded after login.
xession-errors:
X Error of failed request: BadWindow (invalid Window parameter)
  Major opcode of failed request: 3 (X_GetWindowAttributes)
  Resource id in failed request: 0x1800003
  Serial number of failed request: 100
  Current serial number in output stream: 101

$ ps aux | grep compiz
1000 15615 0.0 0.0 7632 924 pts/0 S+ 22:54 0:00 grep --color=auto compiz
$ ps aux | grep metacity
1000 15617 0.0 0.0 7632 924 pts/0 S+ 22:54 0:00 grep --color=auto metacity

btw.
no differences between a gconf.dump file before and after the issue.
no changes between .desktop files (mentioned below) before and after the issue.

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Since there're plenty of questions (2004-2010) in englisch and german forums out there regarding 'metacity doesn't start' here is another workaround, which suggest to move compiz.desktop, metacity.desktop, gnome-wm.desktop from .local/share/applications.
http://ubuntuforums.org/showthread.php?s=ab4dcff2b4a107b078c2c0475015a701&t=1304973&page=2