I joined Curves for Women last week and it is awesome!
I've only had two workouts, but I'm hooked. You alternate between aerobic exercise and 12 different resistance machines. The aerobics is done on these little shock-absorbent squares. Most people, me included, just jog in place, although some add arm movements or a little twisting action. I'm lucky I can stay upright. The resistance machines alternate between legs and arms and I can usually get in 12-15 reps before changing stations.
It's fast-paced, the constant movement between stations means I don't get bored, and they've got CDs of upbeat music playing. The workout is over before I even know it and I'm sweating enough to create my own river.
Safety First: There is always a monitor in the room who has been trained to watch everyone and make sure you are using the machines properly. And once per circuit you are prompted to check your heartrate and compare it to a chart on the wall.
It's only $30/month, I can go as often as I want, and the monthly price is locked for 3 years!
This is going to be a very good thing....