I've made a fresh Ubuntu 12.10 install and the Ubuntu Bold font is missing from the font selection screens.
This means that if I try to use Ubuntu Tweak to set the title font for windows as "Ubuntu Bold" it does not appear as a choice.
The actual file is present in
/usr/share. If I use the font in Writer, for example, I can set it to bold without issues.
fc-cache -frv but that's the only thing I can think of.