In a moving car, you will surely have bad reception. Try stopping for a minute or so. Pull off at an exit or rest stop and try again. When you are moving, the angular relationship between you and the tower is constantly changing, thus making data transmission very hard. Much harder than phone.
Angular relationship changing and making reception difficult? I've never heard of that one before, and I've worked in radio for over 25 years.
I chose not to get the iPad 3G, and got the WiFi version instead.
I purchased the Spring 4G Overdrive box instead. Yes, I know it's more expensive, but it works at 4G speeds here in Central CA.
On Memorial Day weekend, my son, grandson, and I went to Fresno. My son was using the Overdrive with his laptop all the way to Fresno. When we left Fresno, my son was on his laptop, and my grandson had my Netbook, both connected to the internet via Sprint's 4G Overdrive. I know my son was only surfing the internet, but my grandson was streaming a cartoon video. They both used it all the way home, a distance of about 60 miles... it never missed a beat, and the video never stopped.
I also hear people in the San Joaquin Valley of CA complain about AT&T, and especially those that live in the San Francisco area.
I believe that AT&T has oversold it's network and needs to invest in it's infrastructure.