I would never consider replacing my Desktop with the Pro. The screen isn't large enough, not enough RAM, and the video card is not made for gaming.
Well I would NEVER try to use that screen as a desktop replacement.. The 4GB of ram are - okay for most task, I have even conducted a Bim Coordination meeting from the surface yesterday at the office.
(if you dont know what a Bim coordination is - think 3D virtual building construction)
The surface handled it just fine. I had 2 larger models open as one, so for the type of thing I do, their onboard graphics is fine. - guys do not underestimate the Surface pro...