Skinner skis are better on ice because the steel edges are closer to the centre of the boot and consequently more of your mass can be applied directly on the edge in a turn. The problem with fat skis is that in order to get a similar edge angle, you have to tip them over farther, which puts your centre of mass way on the inside, decreasing the pressure on the edge, making it a little squirrely.
BTW, most effective width underfoot, for carving, has been determined to be 61-62 mm.
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This is Whistler, I ended up getting my ass whooped by Jon - I fuckin' hate that guy - he always wins.
 - The Dumont (skier commentary in High Five)
Pleeease! If I get into Ski Canada, then I'll be able to get a sponsership, then my parents won't make me finish school.
 - Marmot Basin local