I've been helping the folks at Craft Lake City organize a Sumobot competition which will be held during their DIY Festival. There are 3 categories: R/C humanoid, lego, and mini sumo. Registration will cost $5 per team/competitor. I highly encourage everyone to compete--I believe building a sumobot is an excellent way to either get your feet wet, or put your engineering skills to the test. I plan to hold a few meetups in the near future to help people get started.
Get more information and register here: http://craftlakecity.com/diy-festival/sumo-bot-competition/