I've been going to Curves 3x a week for two years and I've only missed one week when I had the 'flu. I love it as I get a good, low-impact workout and it only takes 30 minutes. I have arthritis in my foot, so I can't do high impact aerobics or walk very far. Another good thing at Curves is that you don't have to adjust the machines. The harder you work the machines, the more resistance you get, so it's up to you what you get out of the workout.
I've had memberships in regular gyms before but have always quit because I felt self-conscious, plus I didn't like having to wait for the machines, but Curves fits the bill for me. I've met some nice ladies there of all shapes and sizes and age groups and the time goes by quickly.
My arms and thighs have firmed up a lot since I started out. My left shoulder was almost "frozen" due to surgery and now I have full range of motion in it. My knees don't hurt any more, probably because I've strengthened my thigh muscles.
Now that I'm starting to lose weight I'm beginning to see more muscle definition appearing, which is great! Don't worry, you won't turn into a 'muscle woman' at Curves
They let you give it a try before signing up, so I would recommend you go and see if you like it first.