Sure have! In fact, I have people who show up with a music stand, sheet music to show tunes and a group of friends. Usually, One person in the party says "we want to hear
(name) sing...here's her music. IT NEVER HAPPENS!, mainly, we're in a restaurant, not a showclub.

I also have numerous people ask to play breaks, before I start, etc. Management asked me to institute a "no sit in" policy, so I avoid the problem. Of course, that means I cannot ask my friends to sit in, and I really miss that.

Russ