After the historical upgrade from Ubuntu 12.10 Quantal Quetzal to Ubuntu 13.04 Raring Ringtail, some programs, like GVim or Firefox do not start when I try to run them from the launcher.
It turns out to be a permission issue, so, all you have to do to fix it is:
$ chown -hR YOUR_USER .gnome2/
$ chown -hR YOUR_USER .gnome2_private/
Replace YOUR_USER with your user (the user you want to launch the app).