I really have no clue on this. There are some terribly annoying bugs, but they either get fixed quickly, or are left because the fix is hard or unknown (e.g. extensions not working on various distributions except Fedora: wtf. no clue if common packaging bug or upstream).
I'm terrible at QA: Always run the latest tarballs, but usually don't even trigger the most obvious crashers. I just rely on following Bugzilla for that (GNOME and Mageia).
I'm aiming at allowing people to follow GNOME more closely. More people tracking GNOME means hopefully more contributors (testers, triagers, and maybe eventually developers).
I do know that new applications take at least a cycle to get better. But we're releasing them early as well (which IMO is good). E.g. Boxes.