I've been hooping for a couple of years now - 20 mins a day. It has definitely trimmed my waist but you won't lose weight, not much cardiovascular benefit either I wouldn't think. I do exercise DVDs also to keep fit/lose weight. I enjoy the hooping but the benefits are limited to giving a more defined waist rather than anything more.
I started hooping about 3 weeks ago and it's definitely helping to tone the old tum. It might not have caused me to lose weight on it's own, but it's kind of set off a domino effect - my tummy feels tighter so I feel loads better about myself, so I am taking more care over my diet which means I have more energy so I want to exercise more (only extra walking, nothing major!). I've lost 4 or 5 lbs since my hoop arrived! Do give it a try