Two greats things added to the 1GHz dual-core Tegra 2 Motorola Atrix 4G (really HSPA+) on AT&T. One, that Android 2.3.4 with the Motorola UI is available for install, however as a manual download and install, rather than an over-the-air-update (OTA). Second is that 1080p HD video playback is now enabled, so your YouTube vids just got better without any hardware changes. Other improvements pertain to the MotoBlur UI, including faster Webtop browsing. You can also allow non-Market apps to get installed on the Atrix 4G, like Amazon App Store.
All the extra info you’d need are at the source links.
Via: Motorola Atrix 4G Update, release notes