Recently I read this question in one of the pages about the Surface hardware around the web and I found the question interesting enough to make me create an account to answer the question. And here is what I wrote:
In my case probably would be easy to say those things that I don't do in my Surface RT.
I have been using for more than 20 years all kind of mobile computers as my main PC, from Laptops, TabletPC, UMPC and Tablets.
When I began using UMPCs I quickly comprehended that those and later on the Tablets are companion PCs, they are here to complement our computing needs in an era of full connectivity and constant communication. And about two years ago I bought an iPad 2 which I quickly converted and my only PC I used at home and that forced me to find workarounds to all the shortcomings of the iPad + the Tablet platform. The solution, very simple, prepare a PC as you home media server. With that PC constantly on I connected my iPad to it to do everything could not be done in the iPad. That configuration is to me the ideal for those willing to forget the idea of having to sit at home on front of a desk to use a PC.
Later last year when Microsoft released the Surface RT I was one of the first ones to get one.
My set up and experience with my ex-iPad served me to overcome the lack of applications in the first few months after the release. So once again I'm using my Surface RT as my primary PC at home, connecting to my Media Server using remote desktop whenever I do tasks that can't be done in my Surface RT. For example, copying and converting a DVD movie to mkv. Why I should even think about using the limited Surface resources for a task like that? Yes, it could be probably done in a Surface RT if the needed Software becomes available but the fact is that you can't pack yet in any Tablet the amount of hardware resources that you can put in any desktop. So it's more logical to just connect remotely to a desktop and from your surface control remotely the tasks/Software needed to copy and convert a DVD. The same thing happen with other activities such as video editing, etc.
Comparing my iPad 2 with my Surface RT, I gained with the RT the control of my device, something that I never fully had in my iPad which I had to constantly jailbreak to have just some control.
I'm enjoying my Surface RT every single day. And I do in or from my Surface RT everything I need to do in a PC.