I tested with a Surface RT, and this works pretty good. Makes it possible to use the tablet like a laptop, IMHO. The pull out mouse tray also means I can use a mouse with my laptop or maybe eventually with a Surface.
If I get a Surface, it will be a development device. I don't really care to develop for more than an hour or so with a laptop, so it will be used most of "docked" on my desktop, but with that tray, I can do the odd bit of development with the Surface in my lap.
I'm still not sold that the Surface is the Win8 device I'll get, though.