After upgrading my IBM X31 Thinkpad to Ubuntu 9.10, I noticed that libnotify (notify-osd) pop-ups were having a visual artifact when rendered that made the text unreadable. After a half hour of searching the net, I determined that this was because my M6 chipset doesn’t support Render Acceleration correctly, and the default xorg.conf file from Ubuntu does not disable that setting for my graphics driver (Radeon M6).
The solution is to add the option:
Option “RenderAccel” “false”
to the “Device” section of your /etc/X11/xorg.conf file.