So I just installed a font called Helvetica Neue, and for some reason I think it got set as my default .. All I did was drag and drop to the font folder.
It's not all sites, But places like Yahoo and IGN as well as some of my Chrome extensions seems to have switched to this font.
When I go to the font settings on Chrome, it shows that I have it set as Chrome's default fonts (Arial, etc ...).
I can't delete it, because it says it's in use. I've tried Personalization > Windows Color > Advanced, but the font selector is grayed out (so I can't change it).