Just two: Chrome and Cairo Dock.
This is an example of what can go wrong: http://askubuntu.com/questions/9793/...in-the-same-pp
Of course, if your PPA doesn't work, you can always compile the program from source. Because of the large amounts of packages already available, you can easily grab all of the dependencies using build-dep and then compile the program from there.
None on my 'real' install of Ubuntu 12.10. In the virtual install of 12.10 I have added the MATE repository to my sources.list. But as it's not hosted on Launchpad I don't know if it's technically a PPA?
"I believe humans get a lot done, not because we're smart, but because we have thumbs so we can make coffee." --Flash Rosenberg
formerly 'known' as Euroman