I'm sure in this jobless economy most people don't remember WHY we have this holiday. Labor Day is an American Federal holiday observed on the first Monday in September (September 3 in 2012) that celebrates the economic and social contributions of workers, but it only came about with a lot of contention, particularly amongst the trade unions and the government. See this link for detailed information.
Labor Day is supposed to pay tribute to the contributions and achievements of American workers. It also symbolizes the end of summer for many Americans, and is now only celebrated with parties, parades and athletic events totally unrelated to the original reason.
Have a safe and fun-filled long holiday weekend.