I had a bit of a rough ride in this morning. I have a bike that until recently wasn't a bike. I threw some random parts on it to make a commuter during our slushy nasty break up season. For the sake of cheapness, it was a put together as a single speed. I have gears on all my other bikes and now I know why. Any one that tells you a single speed is simpler is only telling you half the story. There is definitely less drivetrain to ruin with poor maintenance. However, when my chain tensioner failed halfway through my commute this morning, I was reduced to riding with my right foot on the tensioner (forcing it to produce tension) and my left foot clipped in and spinning circles by itself. The interesting part being I have never had a derailleur fail in this manner. It'll be an easy fix, but it made my morning commute less awesome than it could have been.
UPDATE: The problem was fixed by completely removing the tensioner. I got super lucky in that the gearing combination I chose on my frame just barely fits an exact amount of links (I don't have SS sliding dropouts). The chain is ridiculously tight, but will probably stretch into something reasonable over the next couple weeks. This does leave me in a predicament if I decide to change the cog on the back.