I just got one of these yesterday and thought I'd share my experience with it. It's a DVR my cable company will include with digital cable service for a $12/mo fee. I've been thinking about getting a Tivo or ReplayTV, but getting the unit for basically the cost of a Tivo subscription seemed decent to me. It will record HDTV shows, but since I don't have a HDTV, I could not take advantage of this feature.
In short, the good: Integrates with my cable seamlessly, guide search works well, nice set of inputs/outputs on the unit, features match other DVR units (pause tv, record subscriptions, fast ff, etc), records original mpg stream without decoding/re-encoding, firewire output would allow recording on a PC
The bad: ad boxes to the left of the guide waste screen space, cannot upgrade hd space (I'm renting the unit), menus could be designed a bit better, cannot watch one channel/record another (although there is an rumored automatic firmware upgrade that will fix this).
I wish it was hackable, but it's probably for the best that it's not! I don't need yet another project to work on.