The PPA for CoverGloobus hasn't been working since Ubuntu 11.10, but this doesn't mean you can't use it in newer versions.
If you are using Ubuntu 12.04, 12.10, 13.04 or even Linux Mint 13 or 14 you can use CoverGlobus by downloading the .DEB package
This is version 1.7.3
Download DEB package for 32 bit system launchpad.net/~gloobus-dev/+ar…
Download DEB package for 64 bit system launchpad.net/~gloobus-dev/+ar…
Installing themes is more easy now, just download them and put the folder in:
Right click on CoverGloobus >Configuration > click on the Theme tab and apply your new theme by choosing it from the list
I hope this will be helpful to all