[Motorola Droid Bionic] johnlgalt:
I think you've gotten the gist of the info, but I'll reiterate.

You have to be on .905 to flash any of the current ICS leaks (and there is a 99% chance of that being true with any future leaks / soak tests / final OTA b/c .905 is the current official OS version for the BIONIC.

You can flash .235 off of .905, but once you are in .235, you cannot restore your phone to .905 via FXZ, and you cannot try to fool the system with a simple Nandroid backup of .905 that you restore over .235. The reason is that the update script also looks to patch several things.

First of all, no update script ever includes the boot.img of the version that is being installed. It includes a patch file that requires you to have either the boot.img of the system that you are coming from, or the system that you are going to. Any other version and it throws up an error and does not allow the update to continue. IOW, if, say, leak .241 comes out, and you're on .235, you have no way to getting .241 without using a method to make the .241 kernel. You cannot flash the .905 kernel onto a .235 system - it trips eFuse and bricks the phone. You have no .241 kernel to install b/c, as I said, the update only includes a patch file, not the full kernel.

Second, even provide that you pass that (which in theory you might as you are on a .235 leak with only .905 /system restored from a Nandroid backup, and if the new leak uses the exact same kernel you'll pass), it also verifies every file in /system that it is going to patch, along with every file in /preinstall that you are going to patch. Restoring that Nandroid backup does wonders for having the .905 /system on your phone, but the current leak you are on has already patched several files in /preinstall, so those signatures will not match, and you'll fail the verification step, and ultimately the update will fail.

For the record, a typical FXZ flashes 17 different partitions on our phones. Nandroid backups on the BIONIC typically can only make backups of 3-4 of those partitions. We have figured out ways to grab a few more of them, but we are still stuck at grabbing a couple of them, and there are 4-5 that we cannot grab from our phones at all.

Since the folks with RAZRs went through something very similar in May and June, mattlgroff figured out a way to fool the update into thinking you have all the components correct in place that need to be there, and the update proceeds. Thus far, after bricking my phone trying to FXZ back to .905 / .902, I used a script to get back on .235, then verified that the move to reinstall the .235 leak works. If another leak is found, then I can test the second part of the script, that which allows new leaks to be installed. The script does not allow any older ICS leak to be installed, and currently there is no way to go back to a previous leak nor a previous GB stock FXZ at all. Even if we had a .223X ICS FXZ or a .22X ICS FXZ or a .230/.232 FXZ, they would not work on a phone that has been updated to .235.

That is why we're saying hold off unless you're 100% positive you're willing to accept the risk - this is way beyond the risk associated with rooting your phone. If Motorola makes the next leak force the phone to have components from .905 that we cannot flash into a .235 upgraded phone, I (and several others that have taken the plunge) might be permanently stuck on .235 until an FXZ for a version of ICS higher than or equal to .235 is released. And that typically takes 6-8 weeks.

HTH