I always wondered how the phrase "break a leg" originated. Theater folk are a superstitious lot, and wishing an actor "good luck" is considered bad fortune, so the phrase "break a leg" is substituted.
Wikipedia has a good summary of various theories about the beginning of the theater phrase. Is its origin Greek, Roman, Yiddish? Is it a holdover from the days of vaudeville? Who knows?
In the meantime, I'll just keep saying it as I look forward to another fun theatrical production with some very talented people.