Rooting the Xoom - will this make it ineligible for 4G upgrade?
The question is technical and I'm not sure there is a blanket answer that covers all possible situations. Here's how I understand it, but I'm the first to admit that this is not my area of expertise so pardon the layman's approach.
If your Xoom is due for an OTA update and is not locked and on the expected, standard software, it will be passed over. The working assumption is that if you are on non-standard software, you want it that way and we leave you alone.
If you unlock your Xoom and load non-standard software, you should be able to reload standard software and relock it, so that you can receive OTA upgrades. Barring that, if the Motorola SBF is made available, as is currently planned, you can flash it yourself.
If you're asking if every change made to the device as a result of root can be detected, I don't know. I doubt that there is an answer for that.
From Matt the Moto Xoom Forum Manager
Every device I've had, I've had rooted/flashed/etc day 1 buying it except... the Xoom. While it was possible day 1, I am simply waiting for the hardware update, then I will go to town on it.
Patience is key here, there are zero apps available as is, and there are almost no hacks available yet, so I see no reason to risk my ability to upgrade a device I just spent $800 on until I know hardware wise, it is 100% what I purchased.