I'm of the opinion that everybody, even if you don't need to lose weight or are at a place where you don't care about your weight, should be doing pilates.
My reasoning behind this is this : after doing just one 20 minute dvd yesterday, the tightness in my lower back went away and I was able to stand up straighter for the rest of the day.
The back pain issue could be endorsement enough, but also consider the following: body fat looks less sloppy when it's resting on top of a more toned muscle. Better posture changes the way body fat is carried as well, and will, again, make body fat look less sloppy.
I'm using a $20(can.) kit made by Bally Total Fitness and sold at Walmart. It comes with a balance ball, stretch band and instructional dvd. You'll probably also want a yoga mat. you need to do this in a room with enough floorspace for you to lie down and spead eagle.
The DVD is grainy and apppears to have been made on an extremely low budget. The instructor is Jaimie Grassi, who is not TV-pretty, but who seems to have designed the workout. Jaimie seems to have been given only one take for each segment, at one point she tries to casually correct herself without drawing notice. The lighting is odd and it seems like flash photography is going on during the filming. Whoever put the segments together has made it cut directly from Jaime saying "and now you can relax" from up on the ball to her in a completely different position down on the floor and seconds away from starting a new exercise.
Production quality aside, it's an accessable dvd, and the workout isn't bad.