Most guys on the board will tell you Xenadrine is just another ECA stack, however I happen to love it. Works great for me of course I've already got an extremely high metabolism (?sp?). I use it whenever I've got to drop about 1-2% bodyfat in a month or so, and am already eating clean, and can't change my workouts any (i.e. cardio). I don't like having to put together my own ECA (Ephedrine, Caffine, Asprin) - just too time consuming, so I go with Xenadrine.
Xenadrine is overpriced! There are other products that will help you as much at a lower cost. And dont go to GNC, they will rape you. Tetracal is a new therm. that's been getting great reviews, and "Jacked" is also a new product.