Tipping provides American waiters with an incentive to increase their check average by pushing bottled water, extra courses, expensive entrees and pricey wines and by showing guests the door as soon as they stop chewing.
That's from Phoebe Damrosch in the NYT (via Ezra), arguing for a new policy of set fees for servers rather than tips. We usually think of tips as providing incentive for better service, but yes, there's a perverse side of this incentive structure, too.
Could this be one of the reasons that Americans are over-eating? We have a restaurant culture where servers can only make a decent wage if customers provide decent tips, and such tips are far from guaranteed. If servers' wages were totally divorced from the amount they served us, would our caloric consumption drop?