Motorola has just posted the Atrix 4G Gingerbread update to their support site for AT&T users. Rather than an automatic, over-the-air update, you're looking at a manual download and install -- though some have reported it's appearing for OTA download via the System Updates preference screen.
Is the update worth it? If the release notes are any indication, it definitely is. Motorola has thrown in a bevy of improvements on top of Android 2.3, including enhancements to the Gallery and Music apps, an updated version of the MotoBlur skin that includes a dock and organized app tray, faster Webtop browsing, full 1080p video playback, and the ability to dismiss one notification at a time from the notification tray.
You can hit up Motorola's support page to download the update (which they've pegged at version 4.5.91) to your desktop and move it to an SD card for manual install. Meanwhile we're installing here now - if you do the same, please do let us know how it goes.
Update: We're up on Android 2.3.4 and a visit to the Application Settings reveals the ability to tick a box that Atrix 4G owners have long wanted: "Unknown Sources." Yes, you can now install any app you'd like, including the Amazon App store.