my little brother did that last year b/c the cuffs of his 7 or 8 year old Sears hand me down snowpants wouldn't fit over his old, bulky, boots. It was kinda funny, he was the most poorly equipped kid at the hill but the best skier in his age group.
iv only seen one person (not including total beginers or people who use rental gear every time they go up sorta thing) put there pants above there boots. and he only did that because we went from lunch to the park for one run, and he was lazy as well.
I did it for the start of the year because my pants were so damn torn that if i didnt roll them, they would look like gothic pants and go over the front of my boots so i would look like im hovering over the ground.