Seems like this idea strikes the right kind of good/easy balance which makes it pop up at random places over and over again. I speak from experience, since I've

Seems like this idea strikes the right kind of good/easy balance which makes it pop up at random places over and over again. I speak from experience, since I've also built a site that tries to focus on solving the 1:1 teaching problem ( http://goteachly.com http://goteachly.com ). I never had the time to finish the feature-set and even more importantly, to spend time marketing it. Even though it appears relatively simple on first glance, it's actually quite complex to execute nicely. Especially the incentives part is tricky. http://www.liveninja.com http://www.liveninja.com seems to know what they're doing though, you might want take a look at that.