I don't pretend to be very knowledgeable about Labor history or the origins of Labor Day, but I plan to learn. The U.S. Dept. of Labor website has a short history of the holiday. (If any of you can recommend good books on the history of the labor movement, I would welcome that.)
I hope the holiday tomorrow gives hard-working folks a day to relax, and that we take some time to celebrate the improvements in working conditions (pay, hours, benefits) that labor activists achieved for all of us. Some of these gains may be at risk, and we need to be more vigilant (I include myself here). Labor Day should be more than the last 3-day weekend of summer and a blizzard of sales in every store.