Can you have too many books?

Cleaning my apartment, and I discovered that when I piled up all of my books in my room, I've read/reviewed a lot of books this  year.
Can you have too many books - ask my mom and a couple of friends, and the answer is YES.
I am in the mood to purge my collection, but the thought crosses my mind.
How do you decide which books are "keepers" and which books "go to new homes?"
I mean, there's a few authors, I can read over and over again (novels), and a few non-fiction books that focus on different areas of interest - like my collection of Henri Nouwen, Thomas Merton, Richard Foster and Brennan Manning books.... and books related to a variety of subjects I've "dug into."
I guess I need to go through my books (including those not unpacked yet) and look at each one without emotion.. 
So how do you decide?