This might've been mentioned, and maybe I missed it (please delete if so), but I find this a pretty nifty feature - if you go to the
WhisperSync for Voice page, scroll down to
Find Your Match in the left hand column you can "Check your audio companions" and see which Kindle titles in your library have an Audible WhisperSync match. It doesn't scan your entire library at once, and you have to click 'load more' at the bottom to eventually scan your entire Kindle library.