After upgrading to Ubuntu 9.04 (and using 8.10 before), I noticed that some applications would show garbled fonts, similiar to:

This happened with KOrganizer, Konqueror, and Virtualbox.  Once I realized the KDE connection, I went googling.  Thanks to TheAL76

** Day 2 - on a reboot, the garbled fonts came back.  Going to Applications -> System Tools, I launched System Settings.

Under "Appearance -> GTK Styles and Fonts" - I have tweaked the following.

• GTK Styles:  Use Another Style : Clearlooks (my base GNOME theme)
• GTK Fonts: Use another font : Undotum   (which I think related to the orginal post below).

Under Fonts:   Enabled "Use Anti-aliasing"

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Turns out this is related to KDE apps use of the QT libs to render windows, where GNOME uses GTK.

Open /home/yourusername/.kde/share/config/kdeglobals in your favorite editor.
2. I wanted UnDotum size 10 to be my font, so I added this:

[General]
fixed=Monospace,5,-1,5,50,0,0,0,0,0
font=UnDotum,10,-1,5,50,0,0,0,0,0
menuFont=UnDotum,10,-1,5,50,0,0,0,0,0
taskbarFont=UnDotum,10,-1,5,50,0,0,0,0,0
toolBarFont=UnDotum,10,-1,5,50,0,0,0,0,0

Save off the file, close the app and restart, so far so good for me - no more garbled fonts.