I see a lot of people on this thread have never worked in the service industry. I did for the earlier part of my career while going to school. I cleaned tables, washed dishes, waited, hosted, and worked at every cook station in a very well-known restaurant chain. Not only do servers have to deal with the entitled, smug, and discourteous customers (80%), they have to deal with the cooks and the dishwashers as well as the restaurant manager in order to make sure customers get a certain level of service. The kitchen staff are sometimes worse to deal with than customers, and don't even get me started on the manager. Point being - waiting tables is not an easy job. Standard practice in the US is that wait staff only make a portion of their income from salary, the rest comes from tips. The amount varies based on the restaurant policy, but it is usually around 75%, meaning servers rely on tips to make their full wage. It's the same idea as sales jobs where your income is tied to the amount of product you move, except with servers, it's based on the quality of the meal, how soon it was delivered, and the level of service. The server is completely at the mercy of someone else for the price and quality of the food, wait times, and just about everything else in the restaurant, with the exception of the quality of their own interactions. When tipping in the US, you should keep this in mind. If you get friendly, knowledgeable service, don't punish the waiter/waitress by withholding a portion of their tip because your steak wasn't well done, or your eggs weren't a "perfect" over-well. A usual and customary tip is 15%, and that is what you should tip if you get average service. Good service should be as high as 25%, especially if the restaurant is busy. Also, +Corey Johnson
makes a good point - often a server has to share tips with the bartender and other kitchen staff, some of whom do get fully compensated. Don't be a part of the problem people - learning to be a good customer will go a long way towards getting good service.