Like so many past worms, this one uses a suggestive come-on to lure the unsuspecting into clicking a link, and after some behind-the-scenes shenanigans, it posts a link to the same lure page on the victim's Facebook wall, if the click-happy victim is currently logged into Facebook.
I'm not much of a Facebooker (in fact, only using it for investigating things like this!) but I've heard reports that this is working, as more and more folk's walls start to look something like this: