I don't belong to Curves/Contours myself but used to work out of Curves in Doncaster (Melbourne) seeing clients and got talking to a lot of the women there. They love it there because the staff are very attentive and focused on weight loss. They set goals with you and work with you every step of the way. I don't know about 'Curves' but I do have clients that use Curves and who also have good things to say about it
They like it because it is a 30 minute workout and allows you to get through the process fairly quickly, but what they like most is the support they get from the staff, and the fact that it is a nice friendly and non-intimidating environment.