If you change the font, even to the default font you chose in Preferences, it would not be saved to the next session and this happened to me when the next session was an hour later. Worse of all - when I launched the application the day after I upgraded it, it didn't load the notes even though they were to be found in ~/Library/Preferences/Memoblock Files. I reinstalled the previous version. iMac Intel 10.5.6