Not a member, though friends and I considered it this summer. The facilities look lovely, and they've done a fab job of making it sound a play paradise for adults and children. I also absolutely love the design of the graphics and advertising materials/website - so well done and appealing.
However, it is so ludicrously expensive to join that I honestly can't imagine the place will survive. Even the 'single day' membership was something like 60 pounds, iirc.