Ubuntu 14.04 LTS.
After rebooting my machine following a hang by the Software Updater (updates appeared not to have been installed, but subsequently have been), the system font is appearing wrong (too small, borderline unreadable) in my main user account. It appears correctly if I log in as Guest.
The font is wrong in all window titles, Chromium tab headers and code editor in Eclipse. Haven't tried anything else.
I notice also that I cannot resize the icons in "my" account. They are stuck at what looks like 0.625 (the size I had them before). Resizing them from System Settings -> Screen Display works fine in the Guest account but does nothing in "my" account. This is not a problem for me, they're the size I want them, but possibly provides extra information.
I have downloaded the "GNOME Tweak Tool" and the fonts/sizes it lists are all identical for "my" account and the Guest account. Changing the size of the "Window titles" font has the expected effect in the Guest account, but no affect in "my" account.
Logging out and rebooting do not help.