I predict this model will not work. exchanging currency and exchanging goods are fundamentally different.

there are/were 5-10 projects around. you can find many threads on the topic going back to 2011 or so. mastercoin will be launching in a couple of days. there is ripple as well, which is not trustless in my opinion.

https://github.com/mastercoin-MSC
https://github.com/ripple
https://github.com/bitcoinx
https://github.com/Open-Transactions
https://github.com/p2p/bitcoin-exchange
https://github.com/InvictusInnovations

see also:

http://www.youtube.com/watch?v=4Iir3_dYmK8
http://bitcoin.stackexchange.com/questions/11116/what-is-the-definition-of-a-p2p-exchange