A half-dozen years ago, when the growing complexity of shows like Lost and 24 was making great swathes of prime time all but indecipherable to casual viewers, YouTube emerged as TV for dummies, a gloriously dependable source of old-fashioned cathode idiocy.

Today YouTube still mainlines a vast and indispensable stream of brainless, throwaway entertainment into our culture, but it also has become more focused and ambitious, says Greg Beato.