I've been holidaying in Southern Germany, on and off, for the last ten years. I have some friends there and know some areas well, so I'd never bothered with a guide book in the past. This year I went there for a longer trip and took the Lonely Planet Munich, Bavaria and Black Forest guide with me. I found it to be a complete revelation and I will definitely be taking it with me on all future trips.
When it talked about areas I'd visited in the past I thought the info and recommendations were spot on, and it also opened my eyes to a whole host of new places I'd never been to previously but will definitely visit again. It is well laid out, easy to read and informative. I now know exactly where the black forest gateaux was invented, and they still make it to the original recipe in the original cafe! The guide also has some great walking recommendations, and cultural highlights to experience (the Fasnet festival is brilliant - why has nodoby mentioned it to me in the past?!).
Highly, highly recommended. Buy it now!