The good part about PPA's are that they can be ignored completely. After being bitten once or twice, I have stuck to not installing anything that isnt in the core ubuntu repositories.
In my 6+ years of using Ubuntu and derivatives, and frequently installing PPAs, I've never had a problem or been bitten. And I've only exercised a little bit of caution.
On the other hand, I ran into massive headaches when I used to try to pin apt repositories. No more of that for me.
PPAs are the main reason I use Ubuntu distros now instead of Debian.
