Gnome Shell doesn't load on Xubuntu

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http://askubuntu.com – All these things I have done before on an identical previous installation on the same laptop, and it worked perfectly. So this is very confusing for me: I installed Xubuntu 12.10 on my laptop and have now decided to install Gnome Shell (using sudo apt-get install gnome-shell) for when I want to show how pretty Linux can be to my Mac and Windows-using friends :D Unfortunately, whilst Gnome now appears as a session on the login screen, loading it simply results in a blank desktop with no panel. Is there a Gnome error log somewhere which I can access, or is there a common cause for this sort (HowTos)