>Mounting mics on your head works fine when not moving your head. I have heard too many recordings with cards, close to the >sound source, going out of phase from head movement. Completely wrecks what could have been a good recording.
That's true, omni's are more forgiving with some head movement. However, I find it easier to control head movement than to control the "screamin' cheetah wheelies" that can surround you and ruin a recording even more than some phasing from cards. You can't control the crowd, but more times than not, the cards pattern have saved a recording that would have been ruined running omni's.
Of course, omni's can be real nice if you have a good crowd around you, but that's a crapshoot at best even taping openly.