I had a similar idea where you'd use some blockchain (Bitcoin, Namecoin, whatever) to keep track of your important assets in a decentralized virtual world, as w

I had a similar idea where you'd use some blockchain (Bitcoin, Namecoin, whatever) to keep track of your important assets in a decentralized virtual world, as well as your location. Bitcoin solves the double spend problem, and you could think of your presence at a particular point in a virtual world as "spending" your time. You could use Bitcoin to ensure no user is in two places at once.