Core77 has initiated a "Design Slam" competition open until February 14th.
The concept is to use their discussion boards as an open forum to develop your work in progress. The winner will be judged not only on their concept, but on their participation.

I can't resist the social-experiment of collaborating 24/7 with a worldwide audience of (sometimes anonymous) designers. So my on-a-whim concept has to do with the eBay effect I've blogged about before: Check it out live and see what unfolds!