I'm on 3 and I've also noticed:
occasional glitches in music play back
occasional hangups where nothing happens before a sudden burst of speed. Almost feels like the OS can't handle everything it has to do, not really sure what its using its 4 cores for then! The music glitch often happens when screen off so I'm not pushing the software hard at all. Normally its smoother and more fluid than ICS was but I didn't get the hang ups before
Also battery life is worse, especially with wifi on. Battery just seems to drain fast in standby and Android System in battery stats is much higher than it used to be.
Can't switch off s planner notifications - they keep turining back on.
Thsts it off the top of my head, a little disappointed. First software versions often require patches to improve so I'm not surprised with the glitches. However what worries me is whilst 3 were fast with JB they were useless with ICS updates. If I had to pick, I'd rather get the main software version a bit slower but then get it fully supported than get the new version straight away but not get any patches for it. When 3 finally gave us the ICS patch about 4 updates after everyone else (adding the brightness slider) I saw many imporvements in stability and battery life on my phone. I hope we get the JB updates, else I might have myself a Nexus 4 soon!