The Unofficial Guide Walt Disney World 2013: We got this book hoping it would be slightly useful in helping us pick restaurants for our trip.  If it helped us avoid one bad meal, we figured it would be worth the $20 price tag.
If you are planning to go to Disney World any time soon and they've doubled the price of the book, it would still be a solid value and you should purchase it immediately. Simply put the book is awesome.
Granted a large part of the book is taken up with reviews of hotels, but that doesn't detract from it's worth.
A similarly large section is given over to rating all of the restaurants in Disney World and since the book isn't written or created by anyone actually associated with DW, they can and do tell you when things stink and when you should avoid them. Using it to pick the places we ate lunch and dinner more than covered the cost of the book.
It also reviews all of the rides and shows and tells you which ones are awesome, which ones aren't and which ones haven't been updated since the 80's.
But perhaps the best part of the book is that it tells you what rides to ride in what order.
Wait you say, the book tells me to go ride a certain ride first and then what to do next?
Exactly. And while that sounds like you are having your vacation dictated to you, what it really means is that you will get to ride more rides and see more shows.
For instance, are you interested in riding the Toy Story Arcade ride in Hollywood Studios? If you follow the book (as we did) you end up waiting about five minutes. When we went back later the wait was 110 minutes. 
Evidently, the writers of the book went to the park and watched and rode everything at all times of the day. They watched traffic patterns  and saw when certain rides were busy and when they weren't. And then they put together several different agendas designed to maximize your time riding and watching and to minimize your time standing in line.
We spent six days in the four different parks at DW and the longest we waited (with one exception) was probably 10 minutes. Okay, let me hedge my bets and say 15 minutes, tops.
The book is very clear that to maximize things you need to follow their order religiously and that to deviate means you risk losing your ability to zip from ride to ride and instead get to stand in a queue like a sheep.
And if there are things you want to ride that it doesn't have listed or there are things listed that you don't want to ride, it tells you how to replace and deviate without hosing yourself. Also there are several different agendas to choose from. 
The book claims that it reduces average wait time per day by about four hours. I would have to say that it made it even less for us. On most days we finished everything on the list with hours of time to spare.
Which is why we ended up standing in line for a longer time, once. We had ridden everything and seen everything that we wanted to see at Epcot and it had started raining. So to waste time until our dinner reservation, we waited 20 minutes to ride the ride at the Mexican pavilion.
You could also spend a few more bucks to get more info and updated lists and wait times on their website, but we forgot to do that so I can't tell you how good that was. But I can say that we didn't need it. The book was plenty good.
The Unofficial Guide Walt Disney World 2013: A+
 - They'll be an entire post about eating at Disney World soon.
 - We bought it at Barnes and Nobles, it's actually $5 cheaper on Amazon.
 - No, that's not a typo. The wait was nearly two hours. What's more astonishing is how many people were willing to wait that long.
 - The traffic patterns of people.
 - Spending 1 or 2 days in a park and with or without small children.
 - That's right we were wasting time while at a Disney theme park because we had nothing else to do, in June.