I ride single speed, because they are simple to work on. When needed I can strip my bike down to the bare frame and back together in little over an hour if I wanted to. I've found with the correct gear ratio there is really no need for a geared bike. I just took my single-speed to Frisco, CO and rode to Keystone and *Copper Mountain without much trouble. I would have rode to the Vail pass but I ran out of time. I did gear down for the climbing. Rode a 46 x 19 when I was there.

I have rode fixed in the past, and really really like the connected feel, but hills are a PITA so its a free wheel for me.

EDIT: Copper Mountain not Vail...