I upgraded my MacBook Pro to OS X Yosemite last Friday and almost immediately found an it was incompatabile with many of my fonts, no matter which word processing program I used: Pages 5, Pages '09, TextEdit, Nisus, or Mellel.
Some fonts just would not work properly in it.
So on Monday I went back to using OS X Mavericks.
I fought pretty hard to have the fonts issues solved in Pages 5, and Tim Cook even took note of the issues I raised, but it seems the engineers just don't care about fonts or typography. I give up. I'll stick with Mavericks until the font issues have been solved, which may be never.
If you have observed any problems with Yosemite, please let me know. I will keep tabs on the issue.