For the same common sense health reasons of not sharing my toothbrush with anybody else, I never let anyone use MY mic either. Some people don't understand why I'm so uptight, but I had to learn this from experience. When I started out, I shared my mic with others because it appeared uptight & selfish not to share. It wasn't till I actually caught a BAD COLD & got a throat infection from doing this, which then kept me off stage for over a week that I learned my lesson and now keep an extra mic available for guest singers. For extra insurance, at the end of the gig, I wipe the mic heads down with a cloth lightly soaked with rubbing alcohol (slightly damp, not wet). Health is a #1 priority, especially for a singer who requires their body & throat as the main musical instrument.

As far as 'eating the mic' itself goes, this can interesting vocal proximity effects. Better watch the teeth though.

- Scott