I've just spent a couple of days organising my audiobooks in MusicBee and I think I've finally found a useful Audiobook manager/player for Windows desktop that isn't Itunes.
http://getmusicbee.com/
It's a little intimidating on first install, but it's worth it (and actually very easy to use.) Most importantly, it happily maintains where you're up to for multiple audiobooks no matter how much you switch back and forth between them, or how many files it came in. Such a simple little feature but so few media players on Windows can cope with it. Has all the other things you'd expect (art, tagging, custom tags for managing audiobooks since they aren't music, synching to devices, etc.)
Oh it's a full featured audio/music manager and player too, of course.
I have no relation to this program, I ran across it completely by accident but I'm a happy user after only a couple of days. It's freeware, but accepts donations.