Someone posted a link to a box that you can plug a standard desktop GFX card into and then plug it into a laptop via USB. I am unsure as to where you can buy them though.
I should imagine that 3gb/s would be enough for basic computing, but anyway... it's actually PCI-E, they're just making an external version it. Or at least this is what I heard. And no, there's no way it could be USB...
this pretty much explains the xgp technology. 4gbytes/s is impressive for a any external device. i wouldnt ever dream of trying to game on a laptop but some people do and this should help them out a lot