This is a review of the ninth (October 2010) edition of LP Bangkok.
I've recently purchased this guide and been extremely disappointed. Lonely Planet has really gone downhill in the past few years.
First, this edition eliminates the usual collection of color maps of portions of the city at the back or front of the book. Instead, in its place is a plain paper fold-out map perforated into the back of the book. This map itself is little better than what the tourist office can provide and what this means is that to use the book in daily walks is to carry two different objects, one of which you must constantly fold and unfold. After a few days my map was falling apart. Worse, especially in a city like Bangkok, is the fact that this fold-out map is the only place in the entire book where you can find a diagram of the metro system. In the past maps were LPs strong point.
Second, the repeated griping about how Bangkok is not what it used to be. Bangkok, like all cities, changes, and authenticity is an invented concept. To continually whine about how "old-school" Bangkok is lost is annoying.
Finally, the index is, for some reason, split up into various subindexes - so if you want to look for a particular shopping area, you need to be in the shopping sub-index, rather than the general index; a frustrating and useless trouble that could have been avoided by simply listing places in both locations.
Otherwise, you will find standard Lonely Planet write-ups. It includes all the historic sights in moderate detail, a bunch of hotels (but Trip Advisor will give you more information), lots of restaurants - though there should be more space devoted to street food, and normal write-ups on shopping. The more in-depth health sections that used to be a part of LP guides are also long gone.
Buy it if you have to.