I spent six weeks in May and June 2008 backpacking around Southeast Asia, and this was my primary guidebook. Overall, I found it to be helpful for the macro-level stuff: planning my itinerary, getting a general overview of each country's history, and budgeting.
I give it three stars, however, because although it's unreasonable to expect it to be as in-depth as the individual guidebooks for Vietnam, Cambodia, and Laos, I often found that the authors omitted useful listings for lodging, places to eat, and sites that were included in other books.
If you plan on taking only one guidebook for VN, KH, and LA, this is a good choice. (Another option is Moon, but at the time of my trip it was even more out-of-date than the LP guide.) Just keep in mind that you'll want to refer to other guidebooks, which I found to be readily available from hostels, cafes, and other travelers in this well-traveled region.