I was wondering how this video was done, I don't know After Effects very well but it looks like there is motion tracking involved. http://vimeo.com/36066912
You can use the puppet tool to make a masked out actor sway and fall sideways, but I think in this case they used a wire rig or just a gym mat on the ground as the shadows behind them move with them. Or it could be all post and they are just good with the little details.
