A lot of you have been very excited about the new Motorola Atrix attaining root so you can do a little development of your own on the new dual-core phone. The system dump of the Atrix turned out to not be encrypted which made developers everywhere jump with joy. Problem is, Motorola had a little "development" of their own. Motorola has signed the partitions of the Atrix as they have done in the past with the Defy and others. This means that though you can root the Atrix, the partitions can not be replaced with any custom content. Looks like the Atrix is once again "locked".
Source (XDA)