A few of us here were discussing ppa-purge a few days ago and I had my first experience rolling back ppa today. Half of it worked anyway 
x-swat rolled back without incident but backports failed. I wasn't paying attention when it happened and don't care enough about it to dig into it (yet) but the install failed about as gracefully as I've seen anything fail, honest.
I reenabled the disabled repos and updated apt - no packages had to be changed. I think what failed was a dry run before the actual uninstall but after downloading 203mb of un-ppa KDE it was nice to see the installer fail rather than the system get broken.
When I do this again I'll see if I can be a little more specific on the error thing - if I can't get ppa-purge to work I'll have to clean install rather than upgrade, but that's no real big deal.
cheers -

x-swat rolled back without incident but backports failed. I wasn't paying attention when it happened and don't care enough about it to dig into it (yet) but the install failed about as gracefully as I've seen anything fail, honest.
I reenabled the disabled repos and updated apt - no packages had to be changed. I think what failed was a dry run before the actual uninstall but after downloading 203mb of un-ppa KDE it was nice to see the installer fail rather than the system get broken.
When I do this again I'll see if I can be a little more specific on the error thing - if I can't get ppa-purge to work I'll have to clean install rather than upgrade, but that's no real big deal.
cheers -