I just unbricked my Starting RSD Mode 3 Xoom. I bricked it about a year ago flashing a rogue recovery. It wouldn't go into fastboot mode AT ALL. All it would do was "Starting RSD Mode 3" and then I'd have to leave it off the charger for the battery to die to power it off.
I'd been checking back on Google every few months to try and see if there was any new info on the web. This time I searched for "xoom brick fix" instead of "RSD Mode 3" and I found the Unbrick Cable and ordered from Ebay. It worked
-Unbrick Xoom USB Cable http://www.ebay.com/itm/acc-84-3ft-F...60632413144%26
-RSD Lite v5.7 app on Windows 7 PC