I've taken Pilates class once a week for years. I think it works the core in a way that other programs just don't. And core isn't just the abs - it's the obliques and back muscles too, all the way around! Core work is SO important, because those muscles are used for just about everything we do.
The exercises are deceptive. They look like they shouldn't be that hard, but proper form is everything and if you are doing it properly - OMG, you really feel it! And there are different levels, so you can start at wherever you are and keep challenging yourself as you progress.
So yes, I'm a big proponent of pilates as part of an overall, balanced training program. I wouldn't want to do ONLY that, because I need more cardio and like traditional strength training and yoga and things like that. But once or twice a week, absolutely.