Problem with a rep system, pirateat40 would have had very high rep... until he didn't, after which he doesn't need it any more, so it wouldn't be... helpful
That's very true.
Even i wouldn't trust someone just for his reputation, but it helps.
Maybe we should think about a risk indicator. For example, pirateat40 had all the numbers to steal a large amount of bitcoins... maybe when the signal were there people should have asked him for more trustworthy data about himself?
Maybe then this would go like: Alice lends Bob 20 btc (his risk indicator increases 20 points) so if carol wants to lend bob another 20 btc to Bob, she may think it twice since bob's indicator says that he is gaining incentives to disappear.
Then when bob gives back his 20 btc to alice, his risk indicator decreases 20 points.
But for this, the forum would have to have a system to forward transactions from a bitcoin address to a user address (This is easy to implement using blockchain.info's api)
maybe there is a niche to create a website that does this? What do you think about the system?