OMG! Ubuntu! reports that a new bug fix release of Ubuntu Tweak that offers more dependable purging of PPAs has been released.

Improving the PPA Purge feature, Ubuntu tweak will now relay an error message and stop removal if it encounters packages cannot be downgraded to their pre-PPA-addition versions.

The error message helpfully provides users with a terminal command to fix the issues. Running the PPA Purge tool after this should then result in complete removal.

  Ubuntu Tweak updates makes purging PPAs easier