Both BTCLuke and I require a 3rd party escrow when trading crypto-usd-bonds for USD (except in person). I submit that 3rd party escrow is ALWAYS required when exchanging with 'untrusted' parties when one side of the transaction involves something physical. The only way to avoid the escrow step is if the crypto-usd-bonds were issued by a PUBLIC, trusted, and 'centralized' company.
Oh man your timing bro....
I think I've found a way around the 3rd party in one case. I'm sooooooooo close to having it all documented...
For normal trading, such as buying USD with Bitcoins, or Bitcoins with USD, I'm still planning to use the 3rd party to actually move the values of the currencies after the trade has "been made" in real time.
For purchasing the representation of the USD, I think there is a semi-trustless 2-way exchange option. (Yes, with no central authorities.) I'll detail it in my upcoming whitepaper.