Hello all,
I signed up specifically contribute to this thread. For me, the addition of Audible was the magic pill, it's whats really made me find the Echo everyday useful and valuable. I struggled with this question prior, I thought it was going to be just a curiosity gadget.
You are right that currently there is limited voice functionality controlling your audiobooks with echo beyond playing, pausing and going back 30-seconds. Although I hoped, and what I'm sure is ideal, is to not be forced to use software as a necessary part of using your Echo beyond the initial setup, but for Audible audiobooks you can readily control where Echo starts playing if you use the Echo app from your smartphone or tablet, it gives you the fine control of selecting individual chapters, and even a slider so that you place yourself at a specific place within that chapter. It offers all the control I would think one would want (except custom bookmarks) to eventually make it across to the device and voice control. Also, if you log into your audible account access your library and use the web-player to select and play a book, that will also transfer to the Echo as the book and location from which to start playing. It's a bit fuzzy, and hasn't worked quite 100%, but has been pretty reliable. I'll play a book from a position for about a minute, stop the web player, close it, then tell Echo: "Alexa, read my book." And more than not, it'll pick right up from where I left off from the Audible web player, admittedly a few times it just continued reading the last thing I had playing on the Echo, and I'll have to try again.. just a tad fuzzy.
Hopefully the added capabilities, kinks and quirks are being worked on to bring this device to as near perfect as can be managed. So far I'm loving it..I might have walked the best spy device the NSA could have dreamed off into my private home, but I've adopted a dangerous blissful ignorance and rose tinted glass view apparently because I've just bought my 3rd Echo and now barely use my Sonos gear.
Again, it's not perfect, not by a long-shot, but it's a start good enough to keep me interested.