How to export annotations in iBooks for Mac?
I think there are two options.

This app is still not yet released http://www.compendiumsapp.com/

The other technique involves an app called Digested. I took the hint from here http://computers.tutsplus.com/tutorials/beyond-highlighting-how-to-get-the-most-from-your-annotations--cms-20013 and should work for your other Macs.


  ...sync your iBooks with your iOS device, and use the Digested app to
  copy the annotations back to your Mac. It's a roundabout way, but it
  does work.