Cycle stuff is fine for light skiing to lunch and dicking around.
Wouldn't be caught dead off piste in deep powder without a proper technical outerlayer, snow skirt, integrated pants, proper gloves and a really good helmet. But then I would never hire skis and definitely NEVER hire boots.
Also if it hits -20 or starts throwing down heavy snow you're going to be fucked wearing a jumper/fleece and pipe gloves or endura gloves. Leather or goretex - or leather and gore tex (ftw)..
Remember it's the mountains, not London.
Like everything else, it depends how far you're pushing yourself and the gear.
I must agree... Im not a fan of dying and prefer the correct clothing. Its a bugger being stuck on a chair and freezing your balls off cause you have the wrong kit.