The easiest/most effective marketing tool

Happy employees who enjoy what they do.

That leads them to tell their network of friends about your company and also creates amazing viral opportunities such as this one shown on the Velopig blog (a daily breakfast blog expressing the blogger's feelings through pictures of his coffee and muffin).

Southwest Airlines gives their employees that ability to have fun instead of adhering to a strict corporate code heaved upon them by the higher-ups. The net result is an employee that has found a way to do his job which entertains him and at the same time entertains his audience (Southwest's customers). It's almost a guarantee that a good portion of the people walking off that airplane will then be passing on this unique experience to the person that picks them up and asks "How was your flight?". Great word of mouth marketing through a companies employees.

So instead of the consumers thinking about how little room they have and how they don't get a meal on the plane, they have a positive feeling after being engaged in an out-of-the box routine announcement.