I can't really imagine doing serious work on a 10" screen. Quick edits, surfing, scanning email and dashing off a quick answer, yeah. But a lot of demand for a "full" OS I'm not sure about.
To make matters worse (or to prove my point), I'm working on some NodeJS code which I will be deploying to Azure a bit later. So, my setup:
Macbook Air, Windows 7 in Fusion in Unity mode BBEdit on one desktop Powershell and a couple of other Win7 windows on another desktop
This isn't quick edits here.
That said, my iPad is mostly for consuming data because I haven't found a development paradigm that works for me. I think the same will hold for WinRT. What is not clear about Surface Pro is if it will get only the Metro UI or if it will get "desktop" as well, given it is slated to have an Intel processor.
Work can be done on small screens, the question is, does the type of work you do cater to being done on a small screen. For me, the answer is yes on an MBAir, no (currently) on an iPad, unknown on Surface.