There's quite a bit of crossover, actually. Too few roadies move around on the bike enough, or really throw the bike around. Of course, there is a point where moving around is less efficient, but for technical descending, understanding weight distribution and how to get good traction can be a real game changer. Sometimes, when I've been riding my mountain bike a lot and I go ride my road bike, it's so much easier to corner with that I feel like I'm going 10mph slower than I really am.