After we got hosed by Paypal, I was crying over alternative solutions for creating an escrow solution for our marketplace. These guys saved us a lot of headaches dealing with escrow and helped us get setup at 2 A.M! I was a bit disappointed when the entire setup from registration to implementation to getting paid only took 15 minutes (translation: I was absurdly happy it was working so quickly). I spent the rest of the night removing my ugly ole paypal implementation.
That and their client libraries make it stupidly easy to get setup! Highly recommend it for marketplace startups!