We're working right now with numerous clients, helping them move their television programming to the web – both through streaming video and podcasting. What I've been preaching on the subject is "short." The Internet isn't really a dumping ground for your full length programming. Posting a 30 minute show on the web doesn't necessarily mean you're experiencing "convergence."
Perhaps in the future, when computer/TV/home entertainment centers have become one box, that will be the preference, and people will sit still that long. But for now, people digest online entertainment in short spurts.
The only exception to that rule is podcasting. I prefer them short, but others, like Matthew Phillips in our office like them longer. Matt listens to his podcasts during his commute to work, so he wants them to be at least 30 minutes. I'm more on the A.D.D. side, so I like them short and sweet. It also seems that the younger the audience, the shorter they prefer them. (At least I think young… 🙂
And remember – anytime you change the medium, you change the customer/audience expectations as well as the way it's used. A lightbulb isn't a candle you plug into the wall. A car isn't a horse with wheels. A TV isn't a radio with pictures. And an effective web-based media center isn't simply a website with a bunch of long videos.
Check out this article to see what I mean.