First, i have nothing against a DVR, I rather like them.
The only trouble with a DVR is that it is what is often referred to as fixed disk recording. Once you fill up the hard drive you need to delete something in order to record something more. For people like me that love to store things on hard drive the DVR is not really an option nor is the Tivo since its technologically the same thing.
I have a blueray that can stream things off the internet and record what I see on DVDs if I want and or store them on hard drive. The amount of shows that I can store in DVD is limited to the number of DVDs that I have on hand to store.
If you have a DVR with a USB port on it then that eliminates the fixed limitation on the recorder, as you can keep adding external drives then your collection is limited only by the size and number of drives you have. With the way drive prices are going these days they are getting rather cheap.
Video on Demand is great if you do not watch movies a lot, but if you watch movies like my family does, at least two a day and most times three per day the prices can add up. If I had to pay $1 each times three per day = $3 per day * 7 days a week = $21 a week * 4 weeks = $84 a month - $6 which is what netflix charges for all streaming = $78 more a month than what I am paying now. But that is only for people like my family that watch a lot of movies each day. If you watch one or two than Video on Demand is great.
What I am looking forward to is Google TV, but I don't want to pay $250 for it. My PC is in the basement and my wife is afraid of the basement so I want to hook up Google TV so that she can web surf from our master bedroom.