I'm reasonably familiar with the physics and artistic implications of sensor size, and I know an unsettling number of people (typically Canon or Nikon fans) that don't know why they think 35mm is the perfect size for a sensor, but they know that it is, and they know they need one.

There's two things I love about 35mm - first, along with most numbers used in photography, it shows Americans can cope with (and indeed embrace) metric, and second the origin is a 'let's get 16 frames to the foot of motion picture film' arbitrary decision made in the late 1800's.

That it defines so many amateur photographers' desires 130 years later is perversely delightful.