I just wanted to mention that one of the best Prosper-related web sites has returned from the dead. www.wallofsham.com This ingenious site profiles Prosper deadbeats - borrowers who have defaulted on Prosper loans. The stories of these individuals are real eye-openers, and sometimes just hilarious. If you want to be a successful lender, it helps to understand the deadbeat.
The site temporarily suffers from a few dead links, due to Prosper's recent removal of 2 years of forum content. Don't let that bother you. Much is still intact.
Note added 05/2008: Wall of Sham is again offline. It is sad to see how people fear deadbeats and the laws that protect them.