Rode a 26 inch geared mtn bike for about 3 years. Front and Rear derailleurs were starting to be worn down by all the winter commuting and accidental falls (trolley tracks a few times and an accident). Never moved it out of the one gear that could still be used. Figured I might as well just go SS/FG.

Bought a fixed gear mountain bike(Marin Hamilton 29er ) upon graduating college, never looking back(well I have a track bike too but I never use it). It's simple and light, but very durable (including the many options I have for tire sizes etc).