I have a 921 and its been pretty good for me this past year. But I too am itching to upgrade. I was thinking about the 942, but with the Feb launch just a few weeks away, it really is worthwhile to hold out for a MPEG-4 capable receiver.
We know that MPEG-4 is coming, so a 942 days are definately numbered. Dish might have a decent offer for existing customers, but would it be better than waiting a few months instead? Likely not.
Besides, this new unit supposely has the ethernet connector, so it at least seems to be built to last for a long while. I'm sure Dish is getting ready for multi-year STB migration plan to crank up. I doubt that they would want to come back and replace any post 2005 receivers for any reason while enduring this expensive operaton.
I think that this is why the only new receivers launched are now HD capable. This will also allow them to standardize on only a few models of receivers. Aside from periodic Hard Drive size increases, the 622 may be Dish's only new DVR for the next few years.