Understood, and that's completely understandable as well. You would have two different options. If you have never done it, you will need to access recovery. You will need Droid 2 Bootstrap while you are on GB
for the Droid X. Hit Bootstrap Recovery, then Reboot Recovery. It'll put you in to recovery. From here just hit Backup/Restore and do a backup. Nandroids are saved to your sdcard/clockworkmod/backup directory, by the date. You can either pull that file off your sdcard then open it, partitions are saved in .tar directories, so you just need to extract using a program like 7zip or IZArc and you can see all your backed up files and delete sensitive ones (i.e. ones linked to your Google account).
Alternatively, you can make the backup (do the backup before the next step!
), and while staying Clockwork, you can hit Factory Reset/Wipe Data, and also Wipe Cache. This will auto-scrub all your sensitive information and completely wipe it to out of the box state, but still on .621. You can then create a backup of this version, and after that (and still in the same Clockwork session, do NOT exit until the next step) go back in to Backup/Restore, and Restore your earlier backup (the one you made with all of your data on it). You can then choose Reboot Recovery and you should be back in just how you were.
This is by far the easiest option and *should*
work fine as it did on previous versions of stock GB
(and it does on all custom ROMs) but I also can't gaurantee they the update didn't b0rk Clockwork in its own way somehow (poking around in the update.zip it appears to include a new boot partition iso file and a new system recovery)
I know people have been able to successfully access Clockwork while on .621, but I haven't heard of anyone wiping data and then restoring a backup. It could be completely fine, and most likely is, but just giving you a heads up. Lastly, this is completely optional.
If you don't feel comfortable doing it, don't. But it would be a great service to the Droid X community if you were able to. If not then I can hit up some other people I have noticed cross-forums, there are a few people such as yourself who are currently on .621 with root. However, the sooner we can get it the better, so *hopefully*
we can have a chance of cracking this early. If you don't feel like taking the risk of the Factory Reset, I can ask which files we need (it appears certain recovery files are needed from the nandroid and probably the framework.jar, among others) which doesn't include any sensitive information. So you could (if you wanted) just do the first backup, then go and choose Reboot Recovery and be perfectly safe, and then just shoot us over the needed files, as well.