I'm similar to mwillems, except I'm not interested in putting Linux on a Surface Pro, at least at this time.
I have more of a business background to my usage, with security being important, and I use a range of applications, which is why I haven't moved to a Windows Phone up to now, and probably never will now.
I would use a Surface Pro for Messaging, eMail, Browsing, Banking, Photography including transfers/backup/reviewing/editing/annotating/uploading/sharing, all the Business applications (yes, Office and Outlook), as a 4WD mapping tool while travelling (I would have loved a Surface Pro mounted in my 4WD while touring around Australia. Touch screen goodness, capacity, connectivity.), Videography (last motorcycle trip with about a dozen friends we had 22 HD cameras on the bikes, recording all the time, which needed gigabytes of video downloaded each night. The Surface Pro with attached storage would be perfect. We collected over 1200 hours of video which took a year to distil down to a 2 hour video memory.), Entertainment of all sort especially eBooks, etc.
Basically, a Surface Pro would be a laptop replacement for me, and give me desktop functionality wherever I was, if required.
Most of that I could do on an iDevice (not sure about 4WD mapping software), but I do not like Apple's locked down OS and lack of expansion options (a simple SD card reader built in? A USB port that works with a USB hub? Copy files to an iPad without tying them to iPhoto, just stored on the drive?) at all.
I haven't checked for Android equivalents to do everything I want. Maybe that would be possible.
But I actually know how to make Windows work for me, and I own applications that run on Windows. So yes, a Windows tablet makes a lot of sense.
Microsoft's core business is quickly moving to the cloud and platform agnostic apps - Azure, Office365 etc. - as opposed to the operating environment itself.
Unfortunately I tend to do stuff in remote locations, on the move, where Cloud services don't make sense. But storing and sharing stuff via the Cloud at discrete intervals does. Therefore I'm not a fan of relying on always being connected.