I have just tried to apply the 8.1 preview to my Surface RT 32 GB and get the error “"The update is not applicable to your computer." Not a good start.
Looks like a few folks are getting the same on the Microsoft Surface RT Devices, Microsoft seem to be on the case.
So far I have been happy with my surface and detachable keyboard, it works fine for me I can use a remote desktop and use office with my Skydrive. It is not a device for installing lots of apps but works fine as a remote terminal, Can watch TV, use the included office and keep in touch via Skype.
I will hang in and wait for a solution from Microsoft.