I have an Atrix 4G phone, which came with Android 2.2. I had been waiting for the Gingerbread (2.3) upgrade. When I learned about the upgrade availability from Motorola, the procedure appeared a bit elaborate, and required an SD card to be present in the phone. A file needed to be downloaded and then copied to the SD card for performing the upgrade. I checked various forums, and discovered that the update was also available from AT&T. Best of all, it could be performed directly from the phone using data or Wi-Fi. Just go to Settings > About Phone > System Update.
I tried the AT&T path and the upgrade was simple and smooth over Wi-Fi. All my data and settings (that I have checked so far) are intact and I love the new experience. I struggle to recall any upgrades that have been easier.