4.2.1 worked for the first day for me before falling apart. Cleared cache and then did a factory reset with no change. Almost immediately it would lag terribly. Open the magnetic cover and it would be 2-3 seconds before you could swipe to unlock. Apps sometimes took 5+ seconds to open. Bringing up the app switcher takes several seconds as does the transition. I don't know if there was a difference in my N7's hardware (it was a replacement for a launch unit with washed out screen) and others who haven't experienced problems, but for me, 4.2.1 was an unmitigated disaster. I guess I'll have to make a nandroid of my current state before gambling on 4.2.2. Sheesh...