I've had this book for almost two years now. I originally started out visiting San Diego frequently, and now have lived here in SD for 2 months.
At first I used this book for the map, to learn where things are, and also to compile a list of things I wanted to do. My boyfriend and I usually set out to do one of those things on each trip that I would come to San Diego. This book was so helpful with that - for example on our visit to the zoo reading the top 10 was helpful because it gave me a sense of what the park had to offer, and what was in my own top things to see.
Now that I live here, I still use this book! I brought it with me just last week to Balboa Park, and I also use before I have friends to visit - I'll flip through and think of them and what might interest them. I even still open it up to look at the restaurants, bars, ect. And just as the other people have mentioned, I use the map all the time (And love that they have a flap so you can mark a page with them).
I highly recommend this book! It is my only San Diego guidebook!