Whatever book I have in my hand I first want to have a general idea what the book is about. I then decide whether the topic even interests me.
When I have a question that I go to a reference book for... for example what code do I need to write to get information off my computer in DOS rather than through window I naturally pick up a How to DOS book and photoread that. Because I knew what I wanted from the book I quickly find it.
Usually you have some idea why you are reading or photoreading a book. Stating a clear purpose helps to stop your mind from wandering or getting side tracked 
Alex
