I am an enthusiastic audio book user, and have been using Aduible.com for some time. I love listening to audio books, I listen when I'm walking sometimes, when I'm doing boring things around the house and when I'm travelling. Having an audio book on the mp3 player is great when you are in that exhausted state about twenty hours after you have left home, and you're still in the airplane and you can't read, and can't sleep and the movie is stupid.
The Lord of the Rings read by Rob Ingles is truly wonderful - I encourage everyone to listen to it.
A year ago when I was still working in the States downloadable audio books were just starting to become available in public libraries. I'm waiting for them to be available here. Maybe something that Gulliver should look at?