I've served many at many different places in the US and Canada- both buffet & entree servings in restaurants and banquets facilities. Though the buffet is a different service in that you don not deliver the food, people tend to drink alot more at the all-you-can eat varities meaning more trips to the table, and even more trips yet to clear the people who make "pigs" out of themselves Generally, service standards are more likely to be higher at a plate-service restaurant, but the work can infact be much harder at the buffet. I will tip in the 10-20% range for each type of service-depending on it. Hotels reflect equal tipping, as a banuet server, whether serving food, bussing buffets, or simply setting up coffee-breaks will all split the total 15% gratutity added on.