I read a couple of technical books a month on average - some of the results can be seen the our "book review" and "on the bookshelf" resource pages. I often find going myself going back to a book to look up a piece of information, only to find that I have forgotten which part of the book the information came from. To cure this problem, I note down the most useful points on a Post-it note which I leave stuck on the first page, inside the cover. The next time I pick up the book, all the key points are to hand.
Note added on 28 December 2006: it seems that the eminent British novelist Kingsley Amis had the same idea. An excellent recent biography describes, while, on holiday, how he read all twelve James Bond books while making notes in the front dust-cover.
