looks suspiciously like a passive ground effect device to me, in effect an extra element to the wing. Not surprised the other teams are whining about it, although why only two other teams thought about doing it is odd. I'm not completely au fait with the latests regs on it, but surely Mac and Ferrari must have ruled it out due to technicalities, because I'm sure I've seen something similar before on one of them.
The way I heard it is that the idea was thought up by a couple of engineers from Super Aguri of all teams.
One of those engineers went to Honda/Brawn and the other went to Toyota.
Williams apparently came up with the idea independently.
Thanks for the link Boga - makes you wonder where they got the detail from.