To try to answer more of your questions;
I don't know why some people have been getting the update and others havent.. wierd. But anyone can do the update by either flashing the SBF with RSDlite, or flashing the update.zip in recovery mode.
1.8.3 is the NEXT sequential update for the Atrix. Starting from the 1.2.6 THEN 1.5.7 THEN 1.8.3. YOU CANNOT jump from 1.26-1.83 (according to Moto's website). So you must be running 1.57 in order to update to 1.8.3!
A SBF is a Signed Bootloader File. It is basically the ROM or OS that our phones use. SBFs can be flashed (loaded) onto our phones using a Dev tool from Moto called RSDlite.
The new 1.8.3 update includes Android 2.2.2 which is the next step up from 2.2.1. If you are running 2.2.1, you will be updated to 2.2.2. The 2.2.2 update contains wifi, bluetooth and various other tweeks. The Atrix specifically gets the HSUPA turned on and the audio tweek and a few other minor things.
In order for the
Gladroot method for 1.8.3 to work, you
MUST have been previously running a ROOTED 1.5.7. So after updating to 1.8.3 you lose the root. Simply plug in to your computer. Make sure USB Debug mode is ON and that the mounting mode is set to NONE or this wont work! Then just open the gladroot folder and click afterupdate.bat. Let it do its thing, the phone will reboot then it should be good to go.
AGAIN, YOU MUST HAVE BEEN RUNNING ROOTED 1.5.7 BEFORE UPDATING FOR THIS TO WORK.
If you are
rooting for the first time, it would be easier to use the
gingerbreak method.
IF you are interested in rooting or flashing the 1.8.3 SBF or update.zip 1.8.3 go to the XDA forum
Atrix 4G Android Development - xda-developers and read up on how to do it. Make sure you read carefully and understand the steps There is a chance of borking your phone if you scew up or something goes wrong. So follow the steps carefully, understand what you are doing before you do it, and understand what/how to fix things (if possible) if you do soft brick.
The NDA (Non-disclosure agreement) thing is that when you accept a beta test invitation from moto, you agree to not share the rom or any info pertaining to it. Apperantly someone who was in beta snagged the ROM before moto made it public and posted it on the web. Moto got ticked and started closing the links and informed forum Mods to close threads and links that discussed the ROM or offered it to download. But now that it is public, it is all over the place. So flash and discuss on.