Meanwhile, using bilateral deposits you can insure any sorts of contracts, not just currency exchange. In my scheme scripts are symmetrical: http://blog.oleganza.com/post/58240549599/contracts-without-...
The coolest part is when this sort of thing is used in autonomous programs that randomly connect to each other and establish contracts. In such case there's no place for extortion - there's no human to negotiate with. Based on this idea you can build never-seen before networking protocols. For instance, a micropayment network that propagates IOUs from peer to peer where each pair of peers is mutually insured to repay all accumulated debt when it reaches 50% of insured amount. It'll be like a global distributed clearing house with as little fees as humanly possible (and instant confirmations!).