Is the "hula hoop" good exercise for waist and hips?

Saw “hula hoops” while Christmas shopping the other day, and this brought back memories of my childhood. My sister was really expert at it, and could do all sorts of twirls with it.

Now as an adult, I’m wondering, is it also a good exercise for one’s waist and hips? Are there any gym trainers or physical therapists out there that would care to comment?