One other handy tip I recommend to folks in the States:
if your pizza is late (or your food at a restaurant comes late or undercooked or something), point this out politely to your server and ask them with a grin whether they can give you a deal on the meal.
More often than not, they will. I once got a $16 pizza order for $5 because it showed up almost an hour late, and I've gotten all sorts of free or discounted meals by asking them to make good on a mistake they made.
If they do give you a discount, give 'em a big tip. It's not the server's fault that the food was late or wrong, but it is the server's competence that got you the discount. And you definitely want to encourage servers to give discounts like this.
And even with a big tip (tip based on the full price of the order, not on the discounted price), you'll still be getting a good deal.
(And Dragongirl, no problem -- it's what i get for being impossibly vague in an effort to avoid political discussion

).
Daniel