@Cageybird- I'd have to disagree with you on this one. I used to ski a lot back in high school, and I probably twisted my knee at least twice a year. I felt like there were too many things that could go wrong while skiing, like getting a pole caught on something or landing wrong after getting airborne. Being on two separate skis gave my legs plenty of opportunities to slide in different directions.
When the first snowboard trail appeared at my favorite ski slop, I found that I had much better control with a snowboard. I thought it was more like surfing than skateboarding, actually. I still think snowboarding is less dangerous than skiing, but it's not something that appeals to all ages.