I agree with all the complaints above—and I even have a few more of my own—but I also have a solution that enables us to play audiobooks in iBooks and have the app play them in the right order.
You need to go to iTunes and, before transferring your audiobook files to the iPhone or iPod (if they're already on your iPhone or iPod, delete them and start from scratch), select all the audio files and hit command-I to get information. Make sure the media kind (under the "options" tab) is "Audiobook." Make sure the "Title" field is identical for all files (e.g., change them all to "Shakespeare on Silver Street"). iBooks will first sort by that title; if they're all identical, it will recognize that all those files are associated with the same audio book. Press "OK."
Now select the first audiobook file (e.g., "Shakespeare on Silver Street [Disc 01]"). The next thing iBooks sorts by is the track number, so you need to change all the track numbers to be in the right order. Change the first audiobook file's information to read "track 1 of 13" (for example); you can also change the disc number to "1 of 13," but iBooks seems to ignore that—at least, when I had those filled in correctly, it still played the files randomly.
Click on the next file button at the bottom of that window (it looks like a > shape). Change the next file's information to read "track 2 of [however many files there are]." Continue pressing > and changing the track information until you reach the last file. Press "OK."
When you drag your files to the iPhone or iPod now, they will be recognized by iBooks under the single title you gave them and the track listing in iBooks will be correct.
That should enable you to play the files in the right order in iBooks with the "15-second" forward and backward jumps and with the speed set the way you want it.
But it's a complete pain in the neck, and iBooks is still a terrible, terrible app. Here follows the additional complaints part of this post:
I suppose it was inevitable—ousting Podcasts from the iPhone Music app was one step.
Please, Apple, allow all media kinds to be played in the Music app. Allow users to choose where to listen to their audio files. That will enable playlists of podcasts and audiobooks for continual listening rather than having to start a new track at the end of every track. It will also allow mixed playlists of podcasts, audiobooks, and music. And it will allow smart playlists (for example, one continuing all unplayed podcasts or all unplayed audiobook files).
Come on, Apple. You used to simplify tasks; now you've multiplied tasks enormously.
Next year, I expect, they will release five separate apps for Opera, Country, Bluegrass, Alternative, and Pop. I, for one, can't wait.
Additionally, Apple seems to have turned off the ability to rate its apps. That's one way to raise customer satisfaction—take away the ability to express dissatisfaction!
—Bardfilm