The small sample around me (about 20 users in their 30s-40s, mid-top management types) all move from WIFI to 3G iPads. We're not in US, so I can't comment about the AT&T situation. But from the iPad users I've seen: >90% are happy with their device, brings their iPad on vacation than a note/netbook, and they usually end up upgrading to 3G version if they have the WIFI.