my folks in Upstate NY have an ATT aircard because they cant get cable or dsl, and the dail-up connection was so slow that banking sites were timing out there browsing. According to ATT their house is supposed to be in a HIGH coverage area, for phone, data and 3G, but after using for a couple hours, I soon realized it was not. There are spots in the house, where the aircard would say it has a signal but not be able to transmit or receive anything. It would say that its connected at 3G speeds, but I dont think that the through put was anything close to what you might get on a 128Kbps DSL connection.
I think an aircard is great if you need to use your computer on the go, or if there are no other sources of internet available. But due to the cap in capacity, and there lack of speed, I WOULDNT recommend them for permanent home use.