Here's an example... yeah yeah I couldn't think of anything else, my girlfriend is listening to that song right now and I typed 'i touhc myself' into google.
Have you recently installed any new fonts? Goofy font files (usually living within your home folder's Library/Fonts) are often behind problems like this.
Sometimes font files are poorly encoded, and so the system has trouble telling two different fonts apart because they have some of the same internal identifiers. The conflicts can be a challenge to hunt down, unfortunately.
While you may be able to solve your problems with Font Book I have always been partial to Extensis' Suitcase (now called Suitcase Fusion). That along with the free Font Doctor will permit you to do all sorts of clean up and management of your fonts. It can even repair fonts if they are not too badly damaged.
But no matter what you do be sure that you do not delete or modify your system fonts.
Finally it would be useful to post which OS X version you are using.