I have spoken to customers who swear by the stuff, but I haven't used it myself for any length of time. I experimented with my boyfriend because he exercises much more than I do, and I had him do one tablespoon every morning before his run (about 1000 mg). After the bottle was finished, he said that he never noticed a difference in energy levels or in his weight. *shrugs*
But the people who tend to buy it at the store where I work are usually are doing more weight training. If anything, it wouldn't hurt to try it, right?