I gave up on the audible app today. The crashing subsided with recent updates, but the battery burn is the deal breaker for me. My Lumia 900 can go down to 50% after a 40 minute commute. Also frustrating is the time and clicks required just to resume playing - Launch app (wait), open book (wait), load section (wait), click play (wait), click play a few more times (wait).
I suspect some of this could be blamed to managed vs native code. Perhaps they can do better with native wp8.
WP team should port native audiobook support from Zune devices. I don't need the frills, just quick and easy playback (like podcasts). I'm going back to my Zune device for now. Audible probably doesn't care as long as I keep buying.