I upgraded my 1st get ATV to 4.2.1 today, call me slow I know but I've been busy. Install went fine however Remote HD from my perspective is useless. XMBC/Boxee don't function because of an incorrect path and after I installed Last.fm the ATV boots to a black screen.
I reflashed my ATV to no avail, still boots to a black screen. I created a support ticket but am also posting here just in case you guys are faster than they are. I don't need my wife thinking I'm Tim Allen from Tool Time. :)