I have been watching TV online or via the web. I do not watch any of the normal network TV, or very little of it. I am currently watching House MD on video and have a couple of episodes of TV saved on ITunes. Wired has addressed this in an article.
This is an interesting phenomenon. TV has changed, is changing, will change. We may stop calling it TV in the long run. What will it be called? Vid? I don't know.
TV on demand changes the way we watch in many ways. An example is the ability to watch all of a TV series at one time, like immersion into the series itself. When you watch a series once a week you do not get this immersion. Series could be made differently as well; I am not sure how.