Shady? Ha-ha. That's funny. I wouldn't say that they are shady, but I know what you mean. When I first heard about Curves, I too was skeptical. I mean, exactly how effective can a 30 minute workout can be? I suppose it's better than nothing, and that if it's done consistently, then it would eventually yield results. It's just that I usually think of 30 minute workouts as maintainence, but to lose weight, I think you need to kick it up to at least 45 minutes.
Anyway, Curves has about a dozen facilities in the Dallas area, and I think they plan to add more. I do think they are a reputable company. My understanding is that their exercises are a variation of circuit training, with the multiple stages that were described in another post. I think their target market is overwieight, middle-aged women who would use being too busy as an excuse as to why they don't work out.
I had a friend going there for awhile, but she stopped when she changed jobs and the club was not conveniently located. What my friend really liked about Curves was that it was an all female gym. She said at her size (~18/20), she did not want to work out in front of men. She also liked the short (30 minute) work-outs. She said she did see results, but she had altered her eating too.
Good luck if you decide to pursue it!