3 things that made me almost get rid of all my 2.1 ROMs and stay with Froyo: (I stayed with Froyo on my Droid anyway tho..lol)
chrome to phone, Flash 10.1 and JIT.
The Sounds and Display settings are seperated. Thats a nice lil touch. I guess that will stay the same. The performance boost u can see easy just by running Quadrant and watching how fast it goes thru the first part of the test compared to any phone on 2.1
I like how the Market is setup on 2.2 The comments have its own tab. I forgot when I first used the Market on the X, I thought something was wrong...lol