I rented one of these at Keystone ski resort in Colorado last week and it was an absolute blast. I'll never go back to skis again. The cool thing about Keystone is that they let you bring home-built ski bikes on their slopes as well. I may do a build. On skis, I never did anything more than a blue run. On the snowbike, however, I was able to do black runs and even a wooded trail. If you ever get the chance to try it, I definitely recommend it!
http://www.snowbike.us/e-galerie.htm
http://www.snowbike.us/e-galerie.htm