I'm getting the impression from the level of creative input and discussion regarding p2p exchanges and fiat-to-digital methods that we are getting quite close to a combination of systems that could prove to be the silver bullet on that one.  In particular are an idea from fellowtraveler being provisionally called BMOT and one proposed solution to the fiat -> digital fiat without trust problem even has a 10BTC bounty for anyone who can find fault with it!  It is the brainchild of bytemaster to be found here, having come out of BTCLuke's hot Primer for a P2P Distributed Exchange thread.