Now you can surreptitiously add it to your own sites, joining The Underground Cabal of Mirthful Protectors of the Corn:
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After a user hits the Konami code (up,up,down,down,left,right,left,right,b,a), every other keystroke will add happiness to the world.
You’ll find this website has already been enabled. Try it out. :)
2010.05.29: BoingBoing will probably add it. And yeah this feature kinda triggered a meme. :p
2012.03.22: Gunnar Hoffman wrote a better implementation: http://paulirish.com/2009/cornify-easter-egg-with-jquery/#comment-68011