We've been hearing about a beta test OTA for the Atrix 4G update for about a week but still have no reports of anyone receiving it just yet. We did discover the changelog though, and it has a few things of interest there, notably a "Data Speed Increase" which everyone is hoping will unlock HSUPA on the handset. There is also mention of connection improvements and improvements to cut down on the screen freezing many are seeing. During my time with the Atrix 4G, I found the data issues and screen stutter to be much more aggravating than the lack of HSUPA, so seeing those two addressed is a big plus.
We have our eyes and ears open for more information about the 4.1.83 update, but in the meantime you can check out the change log and discuss what you think it all means in the Atrix forums.