Right. A bit of philosophical background: I like to think of Reality Keys as a certificate authority for propositions. We perform the same role for facts that Verisign performs for identities: We take information that's widely available to humans, and issue a cryptographic witness statement for it that can be understood by computers. Based on that, people can get their computers to do all kinds of useful things, one of which is creating a contract with a crypto-currency.
Interesting concept. I think the word contract is currently being misused though, in various contexts. What I'm missing is a good understanding of the actual things that we want to do with these kinds of systems. For example say I want to create a weather derivative or insurance contract. These will behave quite differently. I'm trying to think where these external state measurements best apply. Prediction markets never took off really, volume on intrade for instance was always quite low. On the other hand the insurance business is 10-20% or more of world GDP. there you want to observe states which are inherently private.
