I was thinking about this:
A simple online service that provides the protection of PayPal, but for Bitcoin transactions. This would allow sellers/buyers to identify themselves and would potentially remove the mutual trust issue (since Bitcoin is anonymous in the first place).

Imagine if every user had a user ID, and every transaction was associated with a transaction ID. If someone wants to sell BTC to someone else without the risk of getting scammed, he could send x BTC to that user ID, where it would go to a dedicated BTC address where the funds would go through the Bitcoin-PayPal service. Then, the buyer could send the USD to the same service to the transaction ID so that all the funds are stored in the service. Then both the BTC and USD could be released instantly and simultaneously, thus removing the mutual trust issue and at the same time preventing transaction reversing.

The protection is there because if USD is not sent to the transaction ID within, say, 24 hours, the BTC would automatically get refunded to the sender.

Thoughts?