Well, the evidence seems overwhelming to the positive of the question. However, I will give my 2¢ as well.
I'm a Shipping System Software Developer. That means I spend/spent QUITE a bit of time on the warehouse floor going live/debugging/making modifications etc. (13 years) The first 2 years I didn't give a rat's *** about comfort and "just did my job", I was 22. At about 25 my feet and knees began to hurt after 8, 9, 10 hour days. Couldn't figure out why, it never happened before!?!?! Then I was placed on an install in an "ergo friendly" envronment, circa 1996/97. I stood for 10 hours straight on a 1/2" mat while working through some go live issues. When I got home I was tired and had some minor pain. The next day, 6.** hours and the same results. The 3rd day we sat and watched as thousands of packages left the building. In the end I BEGGED the warehouse manager to let me cut one of their mats in half. He gave me a full mat for my efforts. I promptly took it home and cut out a 2x3' section and carried it in the back of my car for years. It came in VERY handy and I wasted no time taking advantage of the comfort. Since then the internet has become ubiquitous and onsite go lives/debug/etc have become QUITE rare. However, I still have a mat (not the same one) in the back of my car. I use it as often as I need to and even take it on plane trips w/ me if necessary.
While anecdotal evidence, I can attest to the fact that YES they work. (Mats DO sit infront of my work bench, drill press, and other stationary tools.)