I never sit and read a full strategy guide for my first play-through a game. Any subsequent playthroughs I may look stuff up to see what I missed (usually RPG's). I very rarely touch Strategy guides for FPS's or Action games. I sometimes look it up for RPG's, especially if I've been away for a while and have no clue as to what I was doing previously (for example with Tales of Phantasia I had literally no idea where the hell I was meant to go having not played for over three months).

Edit: I never use official book guides, only online ones.