Watching BitTorrent penetrate the game demo market has given me an idea for a business model for BitTorrent: charge companies for help hosting files via BitTorrent. It could be a consulting business, teaching sites how to set up and run trackers and seeds. Or it could be a service business, running a BitTorrent hosting service for others. You could offer client support, maybe custom-branded clients. There may even be room for proprietary software here: special trackers and monitoring tools.
I don't think any of this would be a huge business, but it'd be enough to fund BitTorrent development. Customers: anyone hosting downloads of more than 10 megs.