Before I went to Mashup Camp, I exchanged emails with Chris Radcliff of EVDB/Eventful, and it was great to meet him face-to-face at camp. EVDB makes an API for managing event, venue, and calendar data, and Eventful uses that API in an events/calendaring/social networking mashup of events submitted directly to Eventful plus those grabbed from other event sites.
Today, I see that Eventful was covered on Boing Boing, which should bring it a huge amount of well-deserved attention. Congrats!