The ppa-purge package available in the official Ubuntu repositories is not multi-arch aware, so purging PPAs like xorg-edgers or gnome3 doesn't work correctly on 64bit systems.
A few hours ago, thanks to Tim Lunn's work, a branch that adds multiarch support has been merged into the main ppa-purge branch, fixing this bug. The fix should be available in Ubuntu 13.04 Raring Ringtail soon, but I don't know if it will be backported for older Ubuntu versions so to make this fix available for Ubuntu 12.10 and 12.04 users, I've uploaded the latest ppa-purge from BZR to the main WebUpd8 PPA.
For those not familiar with PPA Purge, this is a command line tool that downgrades all the packages installed from a PPA to the versions available in the official Ubuntu repositories.
As an example, if you've added the GNOME 3 PPA, using "sudo ppa-purge ppa:gnome3-team/gnome3" in Ubuntu 12.10 will downgrade GNOME Control Center from version 3.6.3 (which is currently available in the PPA) to the 3.4.2 version (which is available in the official Ubuntu 12.10 repositories); PPA Purge will do this for all the packages available in that PPA like Nautilus, Totem and so on, which are installed on your system. Further more, after running PPA Purge, the PPA is disabled, but not removed.
Also see: How To Use A Launchpad PPA (Add, Remove, Purge, Disable) In Ubuntu.
I've tested the latest PPA Purge with multi-arch support on Ubuntu 12.10 Quantal Quetzal (64bit) with the xorg-edgers PPA and I can confirm that it now works as expected:
Install PPA Purge with multi-arch support in Ubuntu 13.04, 12.10 or 12.04
To add the main WebUpd8 PPA and install PPA Purge with multi-arch support in Ubuntu 13.04 Raring Ringtail, 12.10 Quantal Quetzal or 12.04 Precise Pangolin, use the following commands:
sudo add-apt-repository ppa:nilarimogard/webupd8 sudo apt-get update sudo apt-get install ppa-purge
If you don't want to add our PPA, you can download the PPA Purge deb file from HERE.
Using PPA Purge is pretty straight forward. Simply run the following command:
sudo ppa-purge ppa:someppa/ppa
replacing "ppa:someppa/ppa" with the PPA you want to purge, e.g.: "ppa:gnome3-team/gnome3".