I don't see any notable bugs in my 721. Sure, it lacks NBR and will never get it. But I'll use that 721 until they change everything to 8PSK/MPEG-4 or it turns into dust.
When I had the 522, it had *frequent* audio/video sync issues. What I found was that doing a warm reboot (hold the power button down for some length of time) at least once a week really seemed to eliminate the problem.