A while ago I took out a trial on Audible, Amazon's audio book service.
I got a free book (The Jeremy Deaver Bond - Carte Blanche) and then, forgetting to cancel it, I had to pay £7 or so for a month's subscription, so got a Milton Jones 'audio book' - more a radio show really.
I then cancelled it as I wasn't using it (and I was rather frustrated to find I couldn't stick it on my MP3 player or a CD in the car - Seems you can do the latter somehow now), but in recent weeks I decided to give the Bond book a go.
Half way through and I think I can categorically say Audible isn't for me (probably Audio books aren't).
Reading is a pretty focussed activity. You can't watch TV and read a book, or hold a conversation and read a book. You might do both in a period of time, but you timeslice, breaking from the book whilst you talk or listen to someone and then picking up where you left off.
With an Audio Book I find a distraction takes my mind away from the 'book', but when I return to it, it's merrily ploughed on, knocking down a number of characters and demolishing an ornamental wall!
Unless you can focus entirely on the book, you will miss chunks.
Even a train journey has too many distractions - sunsets, nice cars in station car parks, odd looking fellow passengers, newspaper headlines - even an idle thought can mean you miss a character being killed off or some vital part of the plot.
The other thing is the reader. Toby Stephens, a fairly capable actor, reads Carte Blanche in a suitably sardonic style, but when the action moves to South Africa he proves that he doesn't really have a career playing Seeth Ifrikens! His accent is beyond poor and well into laughable (I did actually laugh the first time he spoke in it). When it's going on in your head, the accents are 'right' because you know what a REAL South African will sound like (and it's not Toby Stephens!).
I'm sure if you cannot read books for some reason, poor eyesight probably, audio books are a great way to get access to literature, information and just books for entertainment, but for me they're a dead loss...