A process for turning ebooks into audiobooks for personal use, at least on Mac:

1. Rip the Kindle ebook to non-DRMed .epub with Calibre and Apprentice Alf.
2. Open the .epub in Sigil, merge all the contained HTML files into a single HTML file (select the files, right-click, Merge). Open the Source view for the big HTML file.
3. Edit the source so that the ebook begins with the title and author, then jumps right into the foreword or preface or first chapter, and ends with the end of the last chapter or epilogue. (Cut out any table of contents, list of figures, list of tables, appendices, index, bibliography, and endnotes.)
4. Remove footnotes if easy to do so, using Sigil's Regex find-and-replace (remember to use Minimal Match so you don't delete too much!). Click through several instances of the Find command to make sure it's going to properly cut out only the footnotes, before you click "Replace All."
5. (Ignore italics here; it's added erroneously by LW.) Use find and replace to add [[slnc1000]] at the end of every paragraph; Mac's text-to-speech engine interprets this as a slight pause, which aids in comprehension when I'm listening to the audiobook. Usually this just means replacing every instance of </p> with [[slnc1000]]</p>
6. Copy/paste that entire HTML file into a text file and save it as .html. Open this in your browser, Select All, right-click and choose Services -> Add to iTunes as Spoken Track. (I think "Ava" is the best voice; you'll have to add this voice by upgrading to Mavericks and adding Ava under System Preferences -> Dictation and Speech.) This will take a while, and might even throw up an error even though the track will continue being created and will succeed.
7. Now, sync this text-to-speech audiobook to some audio player that can play at 2x or 3x speed, and listen away.

To de-DRM your Audible audiobooks, just use Tune4Mac.