Does the following exist, and if not, does anyone besides me wish it did? A web site where a mathematician (say) could find other mathematicians who want to study the same book or paper, and arrange to meet via videoconference, and run their own informal seminar around that topic, and then disband when they're done.
The reason I ask is that I have plenty of material I'd like to learn this way. I have an interesting job in industry, with occasional mathematical challenges, but there are more topics I would like to learn outside of work, and that I didn't get a chance to cover in grad school. I live near two major universities, and they do offer some interesting courses I could audit, but I'd rather focus on the exact material I want to learn.
One reason such a site might be successful (or, more precisely, popular) is that I expect academic mathematicians and grad students would find great use for it as well, since it can be hard to branch out to new areas on your own, if your own department doesn't overlap enough. If you have a deep professional network in the math community, you are probably better off, but not everyone is in that position for one reason or another.
I expect such a site, if it doesn't exist today, wouldn't be hard to create. If the videoconferencing portion was done outside the site using Skype or another service, then the site would just have to match up the groups, and maybe offer other features to support a running seminar. It would basically be a specialized social networking site, or maybe even an application within an existing site like Facebook.
UPDATE 1: The more I think about it, the more I think meetup.com is a good fit too, since it already has the calendaring and rsvp-ing features. The downside is that each seminar would probably have to be a separate meetup, and meetup.com is sort of tied to geography.
UPDATE 2: I have spent a lot of time looking for good, free, non-sleazy video streaming services, and I ended up at livestream.com. They have a couple key features. They offer a free plan with a reasonable business model behind it (the "freemium" model with a paid tier and a free tier that shows ads to viewers, though I haven't seen what these ads look like yet). They have Mac and Windows client software that lets you use your webcam OR stream your desktop, the latter of which I think is very important as a replacement for a physical blackboard or whiteboard. The other piece I have been researching is drawing on the screen with a pen. The best solution I have found is slightly sub-optimal: this pen or this one. They are similar in that they are standard ink pens with a wireless transmitter, and you clip a receiver to the paper and then write normally. The notes are either saved as images (the primary use case), or if you have a recent version of Windows, it can activate the pen features of the OS and you can draw directly into OneNote and other similar programs. This latter is what I want -- the seminar speaker can write on a paid of paper, and the remote attendees will see the writing rendered in real time on their screen. The problems are several: the pens cost at least $50-$60, I haven't tested them, reviews are scarce and Mac reviews are even scarcer. Most digital pen enthusiasm is focused on the Livescribe pen, which is strictly for saving notes and audio for later, and does not transmit in real time. Lastly, I also found this chat software that supports audio and a whiteboard, and which is free. By the way, these pens all look really great for students, especially the Livescribe, because it syncs the audio with the notes, so you can play it back and know what was being said when something was written. And you can convert a session to Flash and upload it as a "pencast". I think pencasts could really be wonderful for mathematics presentations that are recorded offline and then uploaded for an audience to learn from asynchronously.