Yeah, I'm not thrilled about that either...(I've had to leave it running while doing something else a few times too, though usually when we sit down to watch something On Demand, we've put aside a block of at least a couple of hours.)The thing that I really don't like about watching shows OnDemand is that there is a limited "rental" period, so if you only have time to watch 1/2 of an episode, you have to get back to watching it and finish it within a day. Otherwise, you have to start over from the beginning. I usually start the episode and then go do a chore for the next 20 to 30 minutes until I am back to where I left off. Needlessly annoying.
What seems to have become the standard for most networks now (except BBC America, which still allows fast forwarding of its programming

In my opinion the worst one has become CBS, which runs some really insipid PSAs during their reduced commercial breaks. Some of those are so annoying I'd just about rather have to watch the shows with the full count of original ads then have to keep sitting through them.