My family has a ReplayTV, a similar device. We've upgraded the hard drive in it (from the original 30 gig/hour) twice so far as bigger drives have gotten cheaper, and we just got a newer model that has progressive out (still doesn't record HD) and an ethernet jack for transferring shows to our computer.
Personal Video Recorders are one of those things that sound kinda dumb if you haven't seen one in action yet, but once you have it, you'll ask yourself how you lived without it. It has nothing to do with archiving shows for millenia, it's about watching TV when YOU want, not when the schedule dictates. The only stuff I watch when I have my replay is stuff I want to watch. I never have to settle for some half interesting show while waiting for the next good one, and consequently, I think I watch less television.