Well, I used Calibre 2.3 running on Mac OS 10.7.5 (Lion) and converted about 150 AZW books to EPUB without a problem yesterday and today. From what I understand, Mac OS 10.8 (Mountain Lion) was mainly a "clean up" release ala "Snow Leopard" (10.6). The major changes were held for Mac OS 10.9 (Mavericks) of which the minor updates were "Bret", "Bart", "Beau", and "Pappy".
