Outside of the United States of America, there isn't much of a tipping culture. In the US though, it's expectation at a restaurant that you tip your server 18% - 20% of your bill.
Jay Porter, owner of The Linkery restaurant in San Diego, challenged that notion and switched from a tipping policy to one of a service charge - every bill automatically had an 18% service charge added to it (in Singapore it's a 10% service charge).
He wrote a series of columns explaining his reasoning for doing so and what some of the ramifications were. Unfortunately The Linkery has recently closed so I'll never get to try it, but it's interesting to see how many of the negative reviews on Yelp were based on having the service charge added.
Jay brought up the point that customers wanted to be able to control the tip because they felt they had power over the servers - they could use the tip to reward or punish the server based on their perception of the service provided. What other job puts the employee in a position like that?