more outdated info
In addition to the outdated info about climbing the pyramids at Chichen Itza, this book also recommended the ruins as Coba as being lightly visited. I just returned from a trip to the Yucatan in Jan 2008 and by 10 a.m. Coba looks like Grand Central Station in Manhattan. Extremely crowded and the narrow paths through the site only emphasize the crowd. Also the Avalon Grand Cancun was listed as beachfront. While technically correct, there is no beach access since Hurricane Wilma in 2005. The Caribbean comes right up to the hotel wall. Closest public beach access is a 20 minute walk and is not open 24 hours a day.

A tad bit outdated, but overall very good
I looked at Fodor's, Frommer's, and Lonely Planet for the Yucatan. I found that Lonely Planet concentrated more so on backpackers, and Frommer's was much harder to navigate. Overall, Fodor's was the best. Some parts are outdated, which is natural in a high tourist environment like Cancun. Some restaurants have been replaced with others, and some prices have gone up than what's listed. Navigation is very easy through the book, the reviews were quite good, and suggested itineraries were very helpful.

Fodors Cancun, Cozumel & the Yucatan Peninsula 2008
We found a few little gems that were worth the price of the book, most notably, a little museum in downtown Cancun. We were the only ones there and we loved it.

Some parts seriously outdated
We just got back from a week in Tulum and Cancun. Visited major archaelogical sites in the area, including Chichenitza. This guide states that visitors can climb the main pyramid at Chichenitza though that has not been the case since 2005 when a tourist died from a fall there (the guide includes an old photo of two tourists descending the steps). The restaurant recommendations in Tulum were also quite touristy and did not represent the best food available there.