I've wanted to make an altered book ever since I encountered my first one about a year ago, created by Donna Kaiser, my thesis advisor in the art therapy program at Albertus Magnus College. I decided that I want to find out more about this artform and then make one myself.
There is actually an altered book society (International Society of Altered Book Artists - ISABA) online, which gave me a little more info about altered bookmaking. It seems like you can do just about anything, as long as you start out with a book and use it as a base for an exploratory art project. Some artists cut and paste and paint, others cross out or add words to the text to create their own story. You can do anything - it's up to your imagination.
I think the process of making an altered book must be a freeing experience, since it veers entirely away from the traditional - "destroying" a book, albeit to create something new. It sounds like a wonderful form of sublimation to me. I hope to find out soon!