On my iPhone 4, the maximum I ever got on AT&T 3G was 4.61mbps down and 2.52mbps up. This was in Ellenville, NY (a pretty small town) with full 5 bars of signal.
In NYC, normally I get about 1-3mbps down and 200-500 kbps up. In midtown Manhattan during workdays I'm lucky to get any Internet connectivity at all, it gets extremely slow, but I do have wi-fi at work, so I don't really care.