BTCLuke and I have been studying the notion of a P2P Exchange and he has created this list of criterion:
https://bitcointalksearch.org/topic/primer-for-a-p2p-distributed-exchange-212841A P2P Distributed Exchange MUST:
1. Be without any central points of failure, since a government or two WILL be coming after it one day. I suggest a Bitorrent-like software schematic.
2. Show everyone a very large number of possible trades to choose from, (thousands?) so assets can form a stable price. (e.g. a Bitcoin is going for $120)
3. Transact trades pretty much INSTANTANEOUSLY, so when you're watching a graph and want to trade at a very specific time you can do so. (This is extremely important for arbitragers and other traders who help keep the price fluctuation down.)
4. Offer Graphs and APIs for for graphing like MtGox does.
5. Have three-user (trustless) trading, so a non-interested 3rd party always hosts the trade between the buyer and seller. (And should provide Escrow too!)
6. Hold and transfer VALUE, not just IOUs. (With Cryptocurrency this is easy... With fiat? Not so much.)
It seems criterion 6 may require an IOU system; however, is there a way to do it without the need for trust? Is anyone activity studying IOUs and methods to enforce repayment without regulation or trust?