The 2012 Bitcoin Mining Contest has ended, Jerbo was the winner.
To participate, setup a Deepbit-compatible miner and email RaT for a unique mining user/pass.
Prize details will follow, but there will likely be more than one winner (1st, 2nd, 3rd, etc.) and how many will depend on turnout. Think of it like a poker tourney.
As far as rules go, there's no limit to how many miners you can have running, and points are completely based on the number of solutions submitted by miners signed in with your ID.
To jump start this contest, there will be a preliminary winner who will receive a pass to Defcon 20 in July. This winner will be determined based on mining score for May and June.