You're surfing on WiFi. Then you go back to surfing on 3G. All of a sudden "twice as fast" seems just as slow.
Sadly, 3G is the best thing about the new iPhone. Yes it has GPS. But I'll forgo the GPS if I can just copy-and-paste text. If you can't edit, you can't write. The inability to perform such a basic function is inexcusable. Apple, pick up the ball.