This is being demoed on my Motorola Xoom running ICS 4.0.4. Although this Easter egg is available on any ICS device 4.0.x onwards.
Note: Jelly Bean has its own Easter egg. (Coming soon! I already updated to Jelly Bean on Xoom)
About the Easter egg:
OK, explaining this one requires a little bit of Internet meme history. The “Nyan Cat” meme started when a sprite drawing of a cat-Pop Tart from a site called LOL-Comics was posted to YouTube, with an accompaniment of sickeningly addictive J-pop singing “NyanNyanNyan”, the Japanese equivalent of “meow meow meow.” The meme exploded back in April(2012), and you’re welcome to check out the video here: