I too waited tables and worked retail for a few years. It gives you a totally different perspective when you become the customer doesn't it.
I was never a waiter, but my first techical support job was for a large chain (that doesn't exist anymore) doing over-the-counter tech support. I met more flaming a-holes in a week than I had in the previous ten years put together. Wait-staff people and other service-industry folk get a lot of sympathy from me, because I know what kind of abuse they have to put up with from the public.