I created a UStream broadcast earlier today to try it out. I'm still figuring out whether it can be archived (i don't think it can), but it's pretty neat. I've seen video feeds before but the idea of UStream is that it is a more informal video feed (actually, this wasn't their original intention, but the community have pushed them that way!).
The live stream is below - i'm not sure whether to reuse the stream or create a new one next time i am on - as there is no archiving there doesn't seem much point in creating multiple channels (unless there is security/chat archiving in place). I'll figure it out.
So, what's it useful for? Well, as a time-windowed channel, loads of things!, But as a less formal stream, i'm not so sure. It is broadcast only i believe, apart from the text chat below it (see the full channel here), so it may be useful for a discussion/overview with customers (a very easy way of doing so as well), a random broadcast for help on some topic (imagine how neat it would be to go from a phone call or text chat to a video broadcast) and some other ideas. Personally, it would be neat to allow my kids to be able to contact me and see me when i'm out of office :)