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 ). 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 seems to know what they're doing though, you might want take a look at that.

Good idea, especially when combined with online learning (cousera, etc.)

A friend of mine in Germany used to meet up with an American studying abroad at his university for 2 hours a week. One hour they'd speak English, the other German.

I imagine it's not that uncommon.

Yeah, it's very common. But it's hard to find people outside your circle of friends who'd like to do it.

Check out http://www.liveninja.com if you both set your sessions for free, you can do this via video chat :)