Depending on where you're at ATT is already overwhelmed. I'm lucky, in Honolulu ATT is pretty solid. Every time I travel to the west coast (LA, San Fran, ...) I understand why a lot of these folks are pissed. Try sitting in LAX and see what good ATT's 3G is gonna do for you there. Felt like my iPhone was on a reeeeeeeally slow dial up connection.
Not trying to start an argument or debate here, just need to point out that ATT is already having issues in some (not all) markets. 3G iPad is only going to make matters worse in those areas unless ATT steps it up.... Any if you in one of those "ATT sucks here" markets feel free to chime in ......
Sorry but I just noticed this is veering off topic, my apologies in advance. I'll shut up now.