We all thought that Verizon would be the one to lock down Android. Verizon chose the other option and allowed Android to breath and mainly left its core untouched. In comes AT&T, first they stripped out Google Search in every area of the device but that's just the tip of the iceberg.
There have been reports that users can't download apps from places other than the Market. Also, you cant remove any of the preinstalled AT&T apps. If you thought Android 1.5 was the worst thing about this phone, think again it's AT&T.