RoboGames entry deadline is May 15
RoboGames describes themselves as "the world's largest open robot competition". They have over 70 different events, including some specifically for LEGO.
Date: Fri-Sun, Jun 15-17, 2007 (LEGO events on Saturday)
Time: Noon - 10pm
Where: San Francisco, Ft. Mason Center, Festival Pavilion
More details here.