Using Kubuntu 12.04 Beta with KDE 4.8.00 (4.8.0 I noticed in Akregator, that the "read" feeds are hard to distinguish from the "unread" feeds. I went then to the font management and noticed that by default the font weight is set to "medium". I did alter it to "regular" and applied the settings. Nothing happened. When I returned back later (after closing systemsettings and opening it up again), I noticed the font weight was again set to "medium" for the general font. For the others all seems to work fine.
Please paste here as a comment the content of your file .kde/share/config/kdeglobals under the [General] section only. I installed the Ubuntu font and it is shown as Regular. See attached screenshot.
Created attachment 69259 [details] choosing the Ubuntu font
waiting for more info about what exactly the bug is
Qt does not know the difference between Regular, Normal, and Medium. Anything which is not bold or italics is considered the same. See bug 103852. *** This bug has been marked as a duplicate of bug 103852 ***
Having disabled now the "medium" font weight solved the problem. However shouldn't kfontmanager know about those font weights meanwhile?