We've had one for the last 3 years. The biggest single saving was for a stay at the Portifino Bay, I'd guess the entertainment rate saved me about $250 alone for that item.
As Julie says, it's possible to pay for the cost of the book just in the fast food items. Jana and I tend to eat out at some of the higher end places, we'd eat at somewhere similar anyway and the "two for the price of one" offers probably save us $20-30 at each restaurant. It helps a lot now I live in the Orlando area to have the time to use more of the restaurant options, but I'd guess on average I saved $200-300 each year due to the book when coming on holiday and maybe a little more now I live here.
I would agree with Julie, I think it's done a lot better, you get better discounts and a wider range of options with the entertainmnet book. JMHO.