Crash on non-US systems
If your computer is set for a non-US numeric system (e.g. you don't use "$1,052,000.94") there was a potential crash related to the way floating numbers were handled. This was fixed in 2.6.7/2.6.8, but if you have preferences from an older version you may need to reset them. The problematic prefs are most likely "Line height", "Typewriter height", and maybe "Preview delay".
Follow the instructions on the following page to delete your preferences, paying attention to the note at the top. I'm serious.... follow the instructions, don't assume you know what you're doing because in this case you probably don't. I didn't. Which is why I wrote the instructions.... Seriously.... ;)