Seems great on my 3G so far! I am loving folders far more than I thought I would! At first I was like...folders? Seriously? But now that I have been able to use them they are GREAT! I even made a folder on my main screen...of which I am very picky about! (Before I had just the right arrangement of apps (color, icon image, etc...) to make it looks great. I know I am weird -_-).
Only problem I have run into is that the Messages app seems kind of clunky. Sometimes the keyboard lags, or when I send a message the send button gets stuck and the app kind of slows down a lot. Weird considering that the phone feels snappier almost everywhere else. Folders work great, the new dock is great, swiping between screens great, going into and out of apps feels a lot smoother. Going to my last page of apps and then pressing the home button to go to my main screen is so smooth that you can see every app page before it gets back to the screen. In 3.0, this transition from last to first was very sluggish and most of the time I didn't see what happened in between going from last to first.
But the messages app just seems so odd! Maybe it will fix itself over time?