Now let me be clear, spinning to benefit your health or to get a toned bikini body for the summer, is A-MAZ-ING. It focus' on your legs, and benefits all parts. With an experienced instructor they even manage to fit in helping your abs too! I have been going spinning with my brothers girlfriend for almost 10 weeks now, and although I lost about half a stone before I started, since I have gone to lose a further stone! I'm so close to my target weight now that I couldn't be happier (of course you need a proper diet with it).
My instructor says that after 15 weeks of Spinning you will have more or less THREE times the stamina you had before! I think that's incredible!
Although it is a very difficult thing to stick to, if you find the right partner and start from the beginning (you do need to build up to manage to peddle longer and faster) I believe it actually becomes quite fun. And it's definitely rewarding when you see that you've burnt 600 calories off in the end!