Heh, what first got me into gaming was the AD&D (1st Ed.) Monster Manual, which I got when I was 10 years old. So many pictures, and so many colored pencils...
Then I realized there were stat blocks & gaming info with each critter, and from those mostly worked out the AD&D mechnaics on my own. It wasn't until a year or so later that I got another D&D item, only this time it was the D&D Boxed Set (black box with red dragon on fron).
Nowadays, though, I limit my book-markings to underlining certain blurbs of text, or boxing in parts that should be boxed in.