we have Tivo - on non-HD TV for many years. It is excellent and far better than the DVRs I have seen - interface is superior - search and program select (i.e. you could do record any program with woodworking in the description, and feel like you are getting the money out of the check you stroke to the cable company every month). Tivo also has some other "extras" (pictures, podcast, Tivo-only programming) but the core function is excellent.
we now have the cable company DVR because we got a HDTV and our Tivo-model would not record HD programming (although they do make HD-Tivo). It is just a pitiful interface, but the quality of HD makes up for that. Personally, I would like to see the cable box makers just pay the royalties or whatever and license the Tivo interface. I have been watching HD-Tivo prices for awhile with intentions of returning to the promised land.
I'm not sure that i watch more TV or less...but do know when I have time to sit and watch TV - I am watching programming I want to watch (skipping through commercials) and not just what I whatever is on or randomly channel surfing.