I think it was originally meant as physical conditioning for dancers, yes?
I've actually seen people use pilates machines (like nautilus, universal, but more based on moving your own body weight and stressing certain kinds of movements), but I imagine most health clubs don't want to shell out serious money on the latest fitness fad unless they have to.
Pilates is an updated version of Yoga. It involves a lot of stretching and a lot of breathing. However, I would advise anyone who tries pilates to do so when he or she is in good shape. Some of the stretches can be very hard to do and an injury could occur. For myself, the purist in me never got into Pilates, so I use Yoga as a supplement to my workouts.
I went to a free introductory class and the instructor explained that the primary goal is to strengthen deep abdominal muscles, the ones that are usually neglected in other types of workout, but they are crucial to good posture and a strong centre. Breathing is extremely important but it is different than in yoga which can be confusing. Some of the exercises are quite hard. But all in all, I prefer yoga.
I went to my first class. It was really good. It concentrates mainly on abs and lower body workout. Which is good for me because those are my strengths. I'm going to continue with this cause it will REALLY flatten my abs if I do it regularly (and I intend to get a 28 inch waist, thank you) because after the one exercise I really felt it in my abs.
I have also tried yoga for the first time, and didn't find it as effective as pilates but it's good for flexibility and relaxation.
Whoever said, you need to be in fairly good shape to do Pilates, I agree. A friend of mine did it and she got got injured in her back cause she's overweight.