About 2 weeks ago...I got a refurb unit from VZW, and had no problem downgrading it and getting back to where I left off with the unit I had to return to stock and send back to Big Red. The refurbished one looked brand new to boot.
Galaxy Nexus - Daily Driver - Paranoid Android 3.56 (05/28 build)
Sony Xperia Play - GrooveIP WiFi home phone / Gaming Device - Rooted Stock GB
Droid Charge - In-car music device - Tweaked 3.2 / Lazarus Recharged Kernel
Kindle Fire - Hashcode Stock JB 4.2.2 / Hashcode kernel
Asus EeePC 900 - Dual-Boot Android x86 4.0 ICS RC1 / Haiku OS
Retired: Droid Incredible 2, OG Droid, OG Droid #2