Originally Posted by seely

Its not the best thing for your fork... snow gets everywhere, so your fork may take on some water. Also, if it is cold, the action of the fork will slow and get sticky and stiff, since the oil thickens. As far as other parts, your derailleur will get packed with snow and crap and become useless in a few miles, your cables will be exposed to moisture and your bottom bracket could take on some water I suppose, as well as the inside of the frame. If you lube your chain properly and often, and take some time to clean the bike up every now and again it should be ok.