I was going to post something about this but thought wise to search for a thread.
I totally recommend this book, I have both the fine dining and the family one.
Family one is great because if you have a family (obviously) which I don't here, or have regular visitors (which I do), then you have all the tours/safaris and whatnot discounted. You also get all the mid-level restaurants and kiosks with some great vouchers.
The Fine dining one is great for me, some great names in there like Almaz (MoE), Nobu and many of the steak places. Also 2-4-1 offers for a number of buffets like Jumeirah Beach hotel, and a couple in Atlantis.
It's paid for itself for me in 2 weeks.
I may be sounding like an ad, but I strongly recommend either of them.