I know an experienced yoga teacher; she's fat. But that's besides the point. The point is it will only help you in the long run. It will also clear your gas bladder, be aware.
Whoops, the question was, "Do you think yoga is useful in weight loss?" Yes, I think it is. It will be very useful when coupled with diet and other various forms of exercise. If you keep to the two methods mentioned, you can either do yoga or do without it-- it will only help, but if you're not feelin it then go ahead and do something else.