Here is a simple guide on how to root the Motorola Atrix 2. On Windows, Linux or Mac OSX.

Downloads:

Root Instructions:
  1. Connect your device to your computer via USB, enable USB Debugging.
  2. Install the Motorola USB Drivers. (Windows Only)
  3. Unzip the Motofail root package.
  4. Execute "run.bat" or "run.sh" from a terminal (on Linux/OSX)

Source: Dan Rosenberg