As far as I know Pilates is great for toning, but not much else. It's not really cardio and it's not really resistance work for building bulky muscles (though it does claim to build long lean muscles) - at least according to one fitness and weight-loss website I go to regularly! There may be other opinions out there. As Karnak said the important thing is that any movement is good movement and if you enjoy Pilates go for it. It's easier to stick to a fitness program you enjoy and Pilates can be very enjoyable! Plus I found it was a good appetite suppressant, like all exercise, so whenever I do a Pilates session I find I want to eat less which is great for losing weight.
And although Pilates is 'only' for toning, it is GREAT for toning! It's brilliant at developing your core muscles which give you better posture, help you hold your tummy in and give you better balance. I have a few Pilates DVDs and they're by far my favourite exercise DVDs.
I say give it a go. It certainly couldn't hurt your weight-loss and you may end up loving it!