Agreed with the posters above! Webinars seem to be really hot right now as more people use them to sell & teach. Model seems to be similar to teleseminars in that they convert really high - I think there may be some psychology in it too- people feel like they've learned something & invested their time so they buy at the end thinking 'OK, now I know how to use this thing they are demonstrating, let me buy it!" And also, seeing someone drawing live on a virtual whiteboard makes you think you are part of the process too...

One of the more effective ways I've seen this used recently is the Plenty Of Fish case study recently put out by the guys at PPCBully- wasn't even live (I don't think), was just a tutorial. Good content, left you wanting more.