If you go to WDW a few times a year and visit a few WDW restaurants it is WONDERFUL!!
As Tiggerlover91 mentioned no need to mention it when making PS. I've mentioned it on occasion to servers at the beginning but they've always told me to wait til the end of the meal. They still bring out a regular priced bill and then take the discount off after (would be easier to do this first, but I do like to have the original price so I can tip appropriately).