IMO the best part of their site isn't the Farecast -- it's the interface for choosing seats. You can see at a glance what seats are available and how the prices compare to face value.
I'm not sure it was that hard to be like, "you know what, I'll do Farecast for sports and concerts" as an idea. It's the execution that impresses me, but the idea was obvious the day Farecast proved that you could pull it off.