In applications like Firefox or gnome-terminal, some characters get randomly broken. Once the application is running, the broken characters are consistently the same - in the screenshot it is the "t".
This happened after installing Ubuntu NBR 10.04.
I have removed some fonts after installation (like korean, chinese, etc. which I do not use), but I don't think it's related:
[11:46:46][giorgio@Tony:~]$ dpkg -l | grep ii | grep ttf
ii ttf-dejavu-core 2.31-1 Vera font family derivate with additional characters
ii ttf-freefont 20090104-7 Freefont Serif, Sans and Mono Truetype fonts
ii ttf-liberation 1.05.2.20091019-4 Fonts with the same metrics as Times, Arial and Courier
ii ttf-opensymbol 1:3.2.1-7ubuntu1 OpenSymbol TrueType font
ii ttf-ubuntu-font-family 0.69+ufl-0ubuntu1 Ubuntu Font Family, sans-serif typeface hinted for clarity