Note from a guidebook junkie
Yep, I love 'em. Many previous posters have made some great points. My next trip is Shanghai in 2 weeks, and my Lonely Planet is already dog-eared. I've ordered the DK and Frommer's too. Got the Pimsleur Mandarin scratch-the-surface course, and a phrase book. Been to the forum here, TA, bootsnall and thorn tree. Does that mean I'm going to walk around Shanghai with my nose in a guidebook? No. But I think I'll have a much better time as a result of the preparation I did. And, as important, the preparation itself was a lot of fun, at least for me. A major consideration for me is the short time I have available for each trip. I just don't have time to bumble around getting my bearings.
Did the same on my trip to Panama last year, still managed to have several unplanned, unanticipated experiences. Knowing the ropes does not preclude spontaneity.
buen viaje