There actually isn't much a generic Windows box can't do. I control my headless mini with Screen Sharing, but I also use LogMeIn, which I hear works better with Windows.
I got the mini because reviews of similarly tiny Windows PCs were at best mixed, with lots of talk of how to configure them to work properly. All I use it for is Handbrake and Home Sharing, both of which are possible with a Windows box.
I almost bought a NAS, but the mini isn't much more expensive than an empty 4-drive NAS, and it can share iTunes video, which none of the NASs can do. At the moment I have a 3Tb and two 1Tb drives hanging off it.