In Ubuntu 12.10 Beta 2, I've tried using Ubuntu Tweak to change the window title bar font, but after it's changed in the application, it's not reflected throughout the system. I've tried different fonts at different sizes with no luck; the window title font and size stay the same.
I know this is a beta release, but all the other fonts change on the system when I change them in Ubuntu Tweak. The other fonts (Default, desktop, monospace, etc.) update when they're changed. Just not the window title bar font.
Best Answer
I would suggest you use gnome-tweak-tool
to change the title bar font. As of this writing, it works just fine for me.
To install
gnome-tweak-tool, run this command: