BitQuest is doing this (check recent coindesk article), however, I'd prefer one where you can buy in. They are free to play but if you built an economy in-game where you could invest in ventures in game and profit from them virtually, you'd really be onto something.
Willing to invest BTC in this idea if needed (and of course under correct circumstances).
Seconded! I love the idea of virtual economies using real money, and Minecraft seems like the perfect way of going about it. The concept of being able to start up a "business" in a Minecraft server and actually getting something out of it is very, very interesting to me.
Am making something like a real, fluctuating currency. Also making a Reseller rank that can get this currency at a lower rate.