yip we started building this but ran out of resources and had to focus on Roomify.

http://www.youtube.com/watch?v=fms9qM7QG9g

Others have tried (eg edufire.com) but using Flash video chat, which is not great. If people are paying for someone's knowledge/expertise it needs to be delivered perfectly.

Roomify is a more generic version. It is a tool rather than a marketplace. In the future we could do something similar to the above and create a marketplace with in Roomify.