Whether raw or cooked, food can be chock-full of dangerous bacteria long before you can smell it. Perishable food (like chicken and other meats) should be tossed if left out at room temperature more than two hours (much less if in a warm room). For straightforward guidelines on food safety and handling, consult the USDA Web site.
Next time you serve a buffet (or eat one elsewhere), bear this in mind. If the food is not kept warm in chafing dishes (or stored on ice, when served cold), it is no longer safe to eat after two hours of sitting on the table.