I don't know why this is allegedly the most popular guidebook to Thailand. It's organized pretty haphazardly (for example, what would be interesting stories--on ladyboys, elephants, etc) are randomly inserted on pages that need filler. I stumbled on some of these at the end of our trip because they were in some random section.
Quite a few places we walked by--especially in Chiang Mai--had "Recommended by Lonely Planet" signs out front and looked like havens for douchebag "farang".
Most of the places we stayed, and some of our favorite parts of the trip weren't included in the book at all (May Kaidee's vegetarian cooking school in Chiang Mai and Bangkok is the best example; Mae Hwang village outside of Chiang Mai which had a sizeable amount of Westerners passing through on their way to jungle/elephant treks; Spicy Villa there; also Centara hotel in Chiang Mai, Anantara Lawanna in Koh Samui). This all makes me wonder how well they do their homework.
Also very short on information about Thailand itself. In a culture that is strongly based on a shared religion (as the book itself states), they devote just a couple of paragraphs to discussing Buddhism. Very little on their art, which was completely disappointing, as it's the basis for the wats.
Quite a few factual inaccuracies also--most notably, that you're forbidden from photographing Buddha. Not true. None of the temples posted this "prohibition", and when we asked, Thais were incredulous that we were told this. There are some rules for how to photograph Buddha (never place yourself or another human higher in the picture frame etc), and it would have been helpful to have included this instead.
Had a bit of a shock also when they referred to ladyboys as "well-endowed dudes" on page 133. This homophobic Western slang would never be accepted in Thailand, and ladyboys and Thais consider them females--and refer to them as such. Another example of frat-boy mentality which we didn't appreciate.
We had a few incidents with wildlife--sea urchin sting, and a fire ant bite. Having them in the book wouldn't have prevented this from happening of course, but it might have been useful information.
Overall, by the end of the trip, we deemed this book useless. We deliberately chose LP because we're young, and wanted an adventurous trip with recommendations a little off the beaten path and fun. Eyewitness guides or Rough Guides from now on; LP sucks.