Do you prefer PPA over core repositories and why or why not? Are there any compatibility issues when using a PPA as there are different distro releases but just one common repository? Where would you normally search for application repositories that are not in the core repositories? I.e., I was about to install Gnome Flashback in Ubuntu 12.04 which is the new classic version of earlier fallback but found that it's only available as a ppa-release and was wondering which one to choose between the two; fallback or newer flashback.