They've already stated that you can climb mountains.
True, it was mentioned when Todd was talking about the level of detail in one of the recent videos, now, I'd imagine you can't just walk up mountains with ease, but that's reasonable, I mean, look at the mountains we've seen pictures of, do those look like something you can just walk up? They have many sheer cliffs, and I'm glad for that, because they now actually feel like mountains, the mountains in Morrowind and Oblivion felt more like very steep hills. Of course, this may somewhat restrict our freedom of movement, but that's a reasonable restriction, I never feel like the game fails as an open world game because I can't walk straight up the wall of a building, I just don't want the game to restrict me in a way that feels artificial, such as what New Vegas did in putting invisible barriers across places you should be able to cross (The borders though don't count as I realize the game needs to keep me inside a finite area somehow, it can't include the whole world as an explorable area.) if it looks like I should be able to reach a place, I should be able to reach it, but I don't mind the game not letting me do so in a way that I should not reasonably be able to take.
Well thats the thing, finite passages restrict my imagination, i like open speaces i can go anywhere i like, i'm not a big fan of linearity, so although we do not agree on which is best, we do agree that there will be less open space to actually move over than in Oblivion?
I'd say we can expect that, though given that Skyrim is supposed to be a mountainous region, I'd say it's pretty reasonable, in fact, it would be a problem if the map was as open as Oblivion as it would mean Bethesda did Skyrim poorly.