I bought a Tivo so that I could "watch TV on my time." While I can't argue that the Tivo interface is superior, the Comcast service is a much better value. I had to spend $250 for the Tivo box then pay another $300 for a lifetime membership (I could've done $10 per month). Hooking up the Tivo was a bit of a pain, and then once it was hooked up, the delay between choosing a channel and the channel actually showing up was driving me crazy.
Then, I bought a new plasma TV with High Def. I needed to upgrade my Comcast service to get the High Def ($5). For $5 more, I got the DVR as well. I was able to record something while watching another program with the click of one button. The topper was that the whole thing was integrated with one box.
For anyone that doesn't already have a Tivo, I strongly encourage you to get a Comcast DVR. Much better value, much easier to operate. Plus, you get On Demand, which will also eliminate the need to have your Netflix subscription.