From my experience:
Beta 2;
Sirius/XM Premium Online would often drop connection and buffer after a few minutes of play on 3G. Relaunch necessary.
IM+ would crash on launch every time.
Twitterific would often have trouble connecting to the twitter server on 3G.
Meebo couldn't possibly run any slower and with more hiccups.
Beta 3;
Sirius/XM Premium Online seems to be keeping its connection just fine on 3G.
IM+ is still crashing on launch every time.
Twitterific seems to be keeping its connection just fine on 3G but I will update if anything changes as I haven't tweeted much.
Meebo is still a little laggy but much, much better. It's very usable now.