I wish that I saved the posting from one of the classical guitar groups. Christopher Parkening tunes his guitar before every song that he performs. He does it not by harmonics, but by pressing the strings down, five frets apart. The difference is that he tunes either up or down the neck, dependent upon where he will be playing the bulk of the next piece. The assumption is that even the best guitar will be more in or out of tune depending on which fret the string is stopped at.

Personally I just yank the strings lengthwise, if that doesnt work then I pour on the vibrato. But then again, I'm no Christopher Parkening.