I agree that you should file the slips as a personal service to the customer. Giving the slips to the customer means that he/she has to remember to bring them but more importantly he/she could just as well take the slips to someone else's karaoke show!
Kinda self defeating isn't it. The majority of my singers bring their own CDG's to the show and all I need from them is one slip all night with their name on it.
Steve