So what's the deal with Office on Surface?

I am planning to get a Surface PRO in January and I was wondering if it will ship with Office preinstalled and if I could use that Office license to use Office on my desktop PC as well. I am currently using the Office 365 Beta Preview (which I love), but I will have to look for another solution once the preview ends. Do you guys know more about Office and its licensing terms? And how does it look like with Office on the Surface RT?