With Pastime, you simply pick a book to listen to from the easy-to-read list (which shows all audiobooks in your iTunes library), tap the screen to play it (or pause it), and fast-forward or rewind with simple swiping motions. Finding a specific place in the book is easy, and you can't accidentally skip to a place you didn't intend to.
That's it! The font is intentionally large, the control is intentionally simple. To play/pause on the main screen, just tap anywhere.
Update: Now there is improved VoiceOver support.
Update2: Now plays back podcasts as well as audiobooks