I rode a fixed gear on the street in the late 70's, just for training. We knew riding a fixed gear on the 'rollers' (the rolling hills near where I lived) was a 'fast track' to leg strength. I believe the current single/fixed gear fascination was instigated by the daunting complexity of modern bikes. From suspension bikes to road bike drivetrains, riders are saying "enough is too much!" and ditching their bouncy bikes for singlespeed 29ers, also ditching the 9/10/11 (where does it stop?) derailleur madness for a little simplicity. Who hasn't heard "your shifter (or cassette or chain or suspension??) is obsolete! You see, all these components work together, and you now need to replace your whole drive train", which naturally costs more than the bike is worth. So now that shimcampysram has changed the drive train (again) you 'need' a whole new bike!!
Oh yeah? So we all rebelled and started thinking outside the 5/6/7/8/9/10/11 box! My next question- how can megacorp's marketing geniuses make our singles and fixies obsolete? Stay tuned, I bet they've already started!