Did you make sure 3G was turned on/enabled? For some reason when I upgraded to 3.0 on my 3G, the 3G setting was turned off. I turned it on, then put the phone into airplane mode, then back out of airplane mode, and it picked up the 3G in a few seconds. If that doesn't fix it, I'd probably go the restore route as Tramain suggested. Also, did you try rebooting your phone?