Costa Rica is changing very rapidly, so it is very difficult for any guidebook to be up to date, and I am not a huge fan of travel guidebooks. But I usually carry one, and I found the maps, hotel recommendations, and how to get there and away very helpful.
I have met a few guidebook authors during my travels, and their budgets and time allotments do not allow them to check all of the hotels and restaurants. The other problem with Lonely Planet and other popular guidebooks is that many people read them, and the recommended hotels are often full.
The information on Cerro Chirripo was not very accurate, but we managed to find an incredible hostel right next to the trail that the Lonely Planet author hadn't mentioned. The Casa Mariposa offers tranquil gardens and a very homey atmosphere. It was our favorite place in Costa Rica and we spent a whole week there.
The author was also quite negative about the huge amount of tourism and sudden change, but I attend to agree with him, so it didn't really bother me.
My wife and I usually purchase a guidebook when we travel, but we are always alert for other options. Many of the best places that we have found have been by word of mouth from other travelers, or just exploring on our own. But, if you are entering a strange city late at night, or looking for interesting places to visit, this guidebook can be very helpful.Dancing on the Edge of an Endangered Planet