Seems to come from the original game of “Lying Down Game” that is becoming popular in Australia. Someone should write a new meme covering it. I would do it but I suck at descriptions.
News: http://www.youtube.com/watch?v=tRHnTFesv7c (TV news with some planking of there own at the end)
Seems to be picked up by a major commercal radio station:
And finally Wikipedia: http://en.wikipedia.org/wiki/Planking_