I am a HUGE Pilates fan! I like it so much more than Yoga because it's structured differently... so much of the Yoga seems to me wrapped up in meditation and breathing and stuff, and frankly I don't have the patience for that. With Pilates, you do each exercise a few times and move on, so the time goes by really fast and it's really challenging. I've done both mat classes and machine classes, and I think the quality of the class depends on the instructor. I liked my instructor in St. Louis SO much, but the one in Austin is just ok.
Anyway, if you want to check it out, tons of places have classes these days (I took it at my Y in St. Louis and at school here in Austin). Look for somebody who is certified... non-certified people could really mess you up. I'd try to describe the exercises, but it's hard, so I'll just say it works on your abs, thighs, and butt, and who doesn't want those to be a little smaller and more toned?