I ran across it via a Dr. Dobbs article in the fall of 2002. It's like Iron Chef for programmers -- generally. I participated in my first competition about a week after reading about it - it was pretty fun, although my C# was still rusty enough I spent half my time on msdn.microsoft.com reading up on array manipulation and whatnot.
Each single round competition has 3 phases -- 1st is coding, of course. Choose C++, Java or C# (I wish they had Ruby in there...). There's three problems, each more difficult than the previous one. Points are based (for this phase) solely on time. The less time you spend before submitting a solution that merely compiles, the more points you get. But you can only submit once -- well, you can re-submit, but at some pretty severe point penalties. 75 minutes to work these three problems. Problems include sample input and expected output -- but of course they don't give you the full gamut of tests your code will get later.
Then the 2nd phase -- you're put into a room of people in your division (there's a whole ladder system broken into 2 divisions), about 18 people, IIRC. 2nd phase is 15 minutes, everyone can see each other's code ... and can challenge others’ code. If you spot a flaw, you provide input and output that exposes the bug. If you're right, you get 50 points and the coder loses a substantial amount of points, not sure how that's determined. If you're wrong, you lose 50.
Then the final phase is automatic -- their servers compile everyone's code and run it through a series of unit tests -- if you pass all tests, you keep your points, otherwise points are lost.
Wait a little while longer and all the results and stats you could ever want to see are posted at their website -- your code and tests are forever published for all the world to see :)
Then you get ranked on their ladder system through very complicated means based on the performance of other ranked people - blah blah blah.
In addition to the single rounds, they've got 3 day competitions for more established members with cash awards (it appears every single round comp had a purse, but that seems to have dried up this past summer).
The whole deal is actually a glorified job board. The people behind the site think competitions are better than certifications, and they've got some heavy hitters sponsering stuff.
Granted, there's all sorts of skills handy for developing that aren't even touched on -- it's low level algorithmic writing against the clock -- but it all seems pretty slick to me.