This is a list I've sent to a couple non-obsessed friends - apologize for posting things that may already be posted here (I did a quick browse of the thread) or things that are obvious with 2.2. I realize some of this is relative to my phones previous performance and may not be reflected for all.
-Faster overall
-Browser definately faster
-New gmail app is awesome - which is available in market after you get 2.2. Which includes select text in email, and view quoted. and onscreen controls stick.
-Got the quick launch buttons back that the D1 had, where you touch a contact picture and it gives you the popup of options, love it
-New lock screen and new incoming call screen - looks tight,
-8 most recent apps now rather than 6
-New gallery look, vids get own spot too.
-New camera/vid look, and the dead pixel bug that I and some others got on the 2.1 update is gone now
-Gew gtalk look is cool, different color scheme
-Gask manager in 'manage applications' now, which is great. Can kill apps without Advanced Task Killer
-Gattery manager has pretty new look
-Display rotates both ways in apps now (most)
-Boots much faster, much.
-Glash! Just google "flash games" and have fun!
-Market is of course different, but much slower. much. I hope it's because everyone is checking stuff out. Auto update options, etc.
-Google earth feels so much faster
-I dont know if "rss feeds" was an option in the browser before or not but now I've noticed I can subscribe to sites rss/atom
-HaveIi mentioned things are faster? (Except scrolling through home screens that seems to have been slowed down a bit, but clearly not processing problem)
-My "use gps" setting for the weather widget now works, before it didn't and I just had to put in zip code
-Power control widget.. the brightness toggle now cycles through 'auto' as well as low med high
-Can customize what is searched now, all vs web vs apps!
-Wifi supposedly fixed, have not verified.
-The news and weather app/widget from droid one! I missed this so much
-Calender is prettier
-Slide to unlock lag slightly better. .
-Chrome to Phone in market now - which is awesome.
-Sounds are louder
-Exchange works
-Google Voice Search now in market, awesome.
-Suggested words on market search
-Haptic feedback weaker (yay)
-Keyboard autocaps a single "i" now
-Was there a .com button in browser keyboards? gone now
-They say battery life seems better, but I'm on my first day of an extended so I don't know
-They say a GPS bug is fixed
-Some bloatware
-Plus all the 2.2 default benefits the I may not have mentioned.