36 is an interesting number since it isn't a power of 2. It factors* to 2*2*3*3, which indicates there will probably be 4 major decisions that Geralt makes: 2 with 2 choices, and 2 with 3 choices. (Or 3, one with 4 choices and 2 with 3 choices, etc). I'd guess that there are probably 2 or 3 major differences in the ending, then minor alterations based on those.
I thought I've seen CDProjekt indicate that the world will have like 300+ possible "end states". Again, if that's say, 320 "end states", that's only like 7 decisions that have some kind of effect.
Either way, the choices in the Witcher 2 were interesting, so I'm looking forward to this.
Keep in mind that even Mass Effect 3 had quite a few different end states besides the dumb 4-way decision at the end. Your actions in the game (and for some things your previous actions) really did make big changes to how the different races stories ended before you got to the pick-an-ending part. It's weird, but it seems like Bioware could have largely avoided a lot of trouble by restricting your final choice by having the game make it for you based on all of your previous actions. Or, you know, by creating a few majorly different final scense, not just colored lights ...
* Look! I used factoring in real life!