We bought an Orlando Entertainment book for our 16 day trip in 2000, and we saved over $200 using the offers. We only spent 7 days doing WDW and the other week we did other things. I ordered it months in advance and was very methodical about finding offers we could use. I purchased an Orlando area street map to help with locations. I went thru the Entertainment book page by page, and kept a notebook of offers that were of interest. We used not only restaurants, but also mini golf and other area attractions as well. When we dropped off the rental car at the airport, I left the Entertainment book on the back seat for whomever might want it!
Most of our WDW trips are only for a week or so. In those instances, I doubt the Entertainment book would even pay for itself.