All font settings are stored in a hidden file in your home folder, called .fonts.conf.
If you remove it (in your home folder, press Ctrl + H, and delete .fonts.conf), and generate a new one, by running, in a terminal instance (Applications > Accessories > Terminal):
sudo dpkg-reconfigure fontconfig
You then should get the usual Linux crystal clear fonts (you actually may need to log out and log back in, but that's it)
" System settings and prefs, however, have long been a cause of friction between Qt and Gtk. Integration with system settings and preferences is critical to the sense of an application “belonging” on the system. It affects the ability to manage that application using the same tools one uses to manage all the other applications, and the sorts of settings-and-preference experience that users can have with the app. This has traditionally been a problem with Qt / KDE applications on Ubuntu, because Gtk apps all use a centrally-manageable preferences store, and KDE apps do things differently."
And is trying to fix it:
"To address this, Canonical is driving the development of dconf bindings for Qt, so that it is possible to write a Qt app that uses the same settings framework as everything else in Ubuntu. We’ve contracted with Ryan Lortie, who obviously knows dconf very well, and he’ll work with some folks at Canonical who have been using Qt for custom development work for customers. We’re confident the result will be natural for Qt developers, and a complete expression of dconf’s semantics and style."