The only problems I've had with 3.0 so far is the SMS lag. It takes anywhere between 5-30 seconds for the app to open, even if there's only a few messages in my "inbox"
I found before OS 3.0, if I cleared out un-used conversations, it sped up. But not the case for 3.0
Also, the landscape keyboard.. It always flips when I don't want it to, and gets stuck. I usually have to go to the home screen, then open said app (sms, email, safari, etc), to have it vertical again.
I've noticed a small decrease in over-all performance as well as when I hit keys to type something, it lags. I'll type really quickly, it won't do anything, then about 3 seconds after, the word appears in the text field.