they are super hard, but look fun.  i tried a few, and kinda did one (my ski was like just at a wierd angle to the rail.  kinda like \| (first line is the angle of my ski and second one is the rail.)   they were doing them on rails that were beside a ledge, so they just kinda put their ski against the ledge and slid down, way easier that way.
Darryl Hunt
aka - highschool
~Phunkin' Phat Phreerider~