I like the idea, especially since I have a 5770 1GB just laying around. Doesn't everybody?
It costs far too much however. I see no reason to spend on anything better than a ATi 5770 for most laptops, and then the dock costs far more than the GPU. At this price range, you can consider buying a high-end gaming laptop (17" Clevo preferably) instead.
I do however prefer the idea of a $50 dock and a $100 GPU to match on a $400-500 laptop.
Regardless, I'm interested, and I'll be keeping my eye out on this.