Matt's (submitter, author) point about pushing something, /anything/ out of the door by the end of the weekend is a great point. I had the pleasure of working with him at last year's SocialDevCamp hackathon and we ended up using MongoDB as a poor man's message passing system. Why not, we were already using it as a document store! Also, researching and demoing APIs that you might potentially use before the hackathon is very important. We wasted a lot of time fighting with OAuth to get Twitter's streams working.

I wrote up some other tips based on my experience at Madrona Startup Weekend in Seattle at http://www.readwritehack.com/how-to-succeed-at-startup-weeke...