You guys have all brought up some interesting ideas. I agree with Al (kbrkr) that when performing from the left side of the stage it makes sense to have the boom coming in from the left and when on the right side of the stage, coming in from the right. I would add that when performing on a grand piano with the lid open towards the audience that the mic stand would best be placed to your left as well, all to best maximize audience-performer visibility. It's performing center stage, and directly facing the audience that brings up the left/right personal preferences.

Though I of course realize what a silly inconsequential topic this is, I still have to admit that everytime I go to see keyboard/vocalist' perform, I'm always checking to see (especially if they are situated center stage) which side of the KB they put their mic stand. So far my observations have been pretty evenly split: 50/50. It's interesting that most people DO seem to have a preference but most can't explain why. Perhaps we should all try an experiment & place our mic stands on the opposite side to what we're currently accustomed to see how we adjust after a week. I guess I could also begin playing the chords with my right hand and the melody with my left hand, but that's 'another' story. - Scott