With the Surface or any other Win 8 tablet it could make a big difference which browser they are using. Even the RT versions ship with 2 slightly different versions of IE 10. One uses the "modern" (aka Metro) interface and has more limited features for "ease of use" and is the default if you launch from the tiles start screen. The other is a full IE 10 complete with developer tools and launches from the desktop. That's what I use whether I'm on my Windows 8 Pro tablet (full i7 processor, HD graphics, digitzer, etc similar to the Surface Pro but Sony and slightly bigger) or on the MS Surface RT (ARM processor limited to apps more like an iPad than a real computer).
Breakdown of Internet Explorer user strings is at
http://msdn.microsoft.com/en-us/library/ms537503(v=vs.85).aspx#UATokenRef if anyone is interested.
As a result of this thread I spent a little time with yesterday's stats on my blog since I was updating my ride reports using my Windows tablet. I use Google Analytics on the site and looking at the stats it does not show a single access by a Windows tablet despite the fact that I was viewing, editing and publishing using one.
All of the Windows OS access are shown as desktop so apparently nobody used a Windows phone to visit the site in the last week which is all I checked. Mobile shows Firefox OS, iOS and Android. Tablet shows just iOS and Android.