Equal temperament of course has its place as does chromaticism, but I think except for keyboard-players, who can't (unless they have split-key harpsichords or such like), even when playing highly chromatic music the best musicians constantly tweak their tuning to produce the most harmonious result - even in "atonal" 20th century music. I haven't got an oscilloscope, nor do I know how to use one, but I think a scientific analysis would demonstrate that top musicians use more than twelve different pitches even in "twelve tone" music.
Certainly, music in awkward keys, such as C major, requires violinists etc. to make comma adjustments all over the place depending on which open string is most prominent at the time - even in diatonic music. Too many "evens" ;-) C Equal temperament (= 1/12 comma meantone) is a microtonal system par excellence (depending on your starting point of course. Mine is just intonation, with 8 pitches to the diatonic octave). To get on or off this list see list information at http://www.cs.dartmouth.edu/~wbc/lute-admin/index.html
