One interesting change that I didn't see any place mention is that you can sync and use the devices at the same time.
Although, I was noticing some bad battery life with my 3GS and I wonder if it's because I left the device as "connected" in iTunes (even though it's not plugged in). My assumption is that it being connected possibly left the WiFi turned on, which would explain why it's gone from 100% to 85% over the past 3 hours (it hasn't really done anything during that time).
EDIT:
I think that is the issue. I "ejected" the device in iTunes about 10 minutes ago ( it disappeared like normal ), and I looked again now, and my 3GS is back in iTunes. :|