Audio books put me to sleep, which isn't necessarily a bad thing. If I am in a situation that requires I stay awake, like the gym, my mind wanders and I lose track of the book. It does make the gym go by faster and more pleasantly, but often I don't absorb more than a few words. It is better on the stationary bike thing, sometimes I absorb 20 pages or so
So while I find them pleasant, it would probably take me weeks to actually listen to a book and feel that I have absorbed it in some way.
Helen