Using Font Book
Mountain Lion & Above
Font Book in Mountain Lion (OSX.8.x) and up are by far the toughest ever on fonts, of any OSX versions. Here are directions for finding Duplicate Fonts:
01. Open Fontbook.
02. In left Pane select all (Command-A).
03. In right pane select any Font.
04. Next hold down Command - A (Select All).
05. Open Edit Menu, look for any enabled duplicates.
06. A window will open listing fonts checked, allow to finish.
07. In the window showing the names, click on the header, All and switch to errors and warnings.
08. Open each font shown as duplicated.
09. Look at the fonts (will show both versions). Choose oldest and remove.
10. Now go to file menu and choose Validate Fonts.
11. Repeat step 7 above.
12. Any warnings delete immediately.
13. With any errors shown, open each, and resolve duplicate fonts, manually keeping the newest.
14. Repeat validating fonts untill nothing shows.
15. Close, and try any applications affected by font issues. If still having issues continue with 16 or 17.
16. Also Check out this link from Microsoft: http://www.officeformachelp.com/office/font-management/
17. Also check out this link titled : Font Management in OS X, by Kurt Lang