Audible.com, the Internet’s premier provider of digital audiobooks and more, is now available on your iPhone and iPod Touch! This free app features the most comprehensive audiobook experience ever, including Wi-Fi delivery of your Audible.com library, multitasking (iOS 4 and compatible device required), detailed listening stats, and more.
You don't have to have an Audible account in order to try the app. (I like that.) I've tried the app, and it's a lot nicer to use than the Overdrive Media Console.
Unfortunately, downloads take a long time and the user has to make sure the app stays open. Both of the excerpts I tried ended up with corrupted files because the downloads were interrupted.
I'd say wait for a later version.