The Ear or the Eye - What makes for a good Audio book?

I joined Audible.com back in May of 2002 and have 304 audio books in my library to date. I listen to audio books while I drive, while I exercise, and if I'm really hooked, I may make up an excuse like cleaning the house to get some extra book listening time in.

I've been thinking a lot recently about what makes for a good audio book. In my experience of 304 books, not all are good for audio. Maybe not all are good for books, but that's not the point. Sometimes a book may be fantastic on the page,