I live in Toronto and I was sick of having my rear derailleur freezing so I went single speed and never looked back. On my first bike I used a White Industries ENO eccentric hub and went about 63 gear inches which was a little tall for me. Irclean hits the nail on the head on trying to mash in too high of a gear makes the bike hard to control.

My next bike was/is a Specialized Centrum Globe singe speed. It is geared lower around 58" and was much better. The disk brakes were a nice touch, so much I would never ride a winter bike without them but this is personal preference.

This year I am thinking of a new winter bike and I may go the Irclean route which is an Alfine, disk brake equipped bike. This way I may get the best of both worlds, no derailleur to freeze and the use of actual gears.

Typically I ride single speed everyday for my commute, so I am biased. I ride a geared bike once every two weeks on Sunday. It will be interesting to see if I change gears much this winter.