Under 3.0, A2DP audio was out of sync with video so often that I could really only use it with audio-only content - using it for TV shows or movies was just painful.
Under 3.1, A2DP is sometimes out of sync but often in sync, and even when it is out of sync, it is off by a smaller margin than 3.0 was.
If A2DP has worked better for you than it has for me, it's probably because you have a 3GS, whose fast processor seems less susceptible to sync issues. But I'm definitely not the only one having audio sync issues with A2DP (check out some of Menny's posts at Brighthand...).
Boot time for my iPod touch under 3.0 was crazy - I'd say about two full minutes. Now it just boots up in a few seconds like most iPhones have normally done.