As for me I've been using my Build tablet for over a year now as my laptop replacement. It works pretty well for development despite the small screen size & resolution. I certainly would prefer the resolution on the Surface Pro however.
I use the tablet mainly as a third screen (mail, web, OneNote) on the desktop using mouse & keyboard most of the time. On weekends and on the road it becomes my laptop but again I use it mainly on the desktop with mouse & keyboard.
Now that I have a Galaxy Note II as a phone I seldom use the tablet as a tablet. IMO this is another example of Microsoft being late to market and not anticipating where it's going. My next laptop replacement might just be a laptop if I can get more power, memory, bigger display, etc. now that my tablet needs are fulfilled.