MTurk is representative of the human population. I hear it often that people presume that MTurkers do not put in any effort for a few cents. But for most it is a hobby/nice pastime. They do it to make a few bucks, instead of playing chess or reading a book. Most people do not get a nickel playing chess, though really put in the effort. MTurkers are similar.

See here for an MIT experiment in blurry text transcription: http://groups.csail.mit.edu/uid/deneme/?p=329 for the unexpected accuracy resulting from crowd-sourcing.