Etoile: Every time I go up to a box office to puchase tickets on the spot (unless it's something like 3 DAYS OF RAIN, PAJAMA GAME, WICKET, JERSEY BOYS, SPAMALOT) I say "I would like to use the playbill discount, please." I always get a discount - whether the ticket is $45 or $75 - I still always get a discount when I say that.
Don't presume anything. Give it a try sometime. Guaranteed it will work - it's never failed for me, and I've been doing it for five years.
"If you are going to do something, do it well. And leave something witchy."
-Charlie Manson