No, no way, nobody's taking my mouse buttons away!
This inteface is all but accurate, it's very limitative.
It'd force the user to use the other hand in situations where only a mouse click would be enough (because it's limitative, it'd need modifiers help to expand it's functions). If not, it'd take much speed away, since the user would have to to a bunch of mouse movements to do actions (which is yet another problem, you'd have to memorize them), or it'd take years to do stuff because you'd have to wait for the buttons to be activated on mouse-over.
I think it's unuseful, unconfortable and limitative. But, the site sure does look good!
PS: i'd love to see them doing a demo of someone using photoshop with that method