just as a quick FYI - I have a Panasonic dual vhs/dvd recorder. i have it set up and record dvds of shows as I am watching them, just as I would have done w/a vhs recorder.
That way I am able to remove them from the Tivo to make space in the HD. I do have to admit I am a bit OCD about keeping shows, etc.
I have had HD failure in the past, so just keeping them stored on the tivo HD is subject to that loss (if you want to keep shows).