I've been running two HDTVs off of one ViP622 for a year now. It works great. I can access all my recordings on one box. No need to set separate timers or worry about which box has which program you want to watch. I can also use my external drive on the ViP on both TVs as well.
I have the ViP box in the basement hooked up to TV1 (50" plasma) via HDMI. I have TV2 (32" LCD) in the bedroom hooked up with 100' of component (+L/R audio) AND coax. 95% of the time the TVs aren't in use at the same time. I run the box at these times in single (mirrored) mode. For the other 5% of the time, my wife or daughter can just watch the SD feed on the coax in dual mode. Works like a charm!