I've got a 12" iBook G4 running the display spanning hack. Right now, I've got a 17" LCD connected and acting as a secondary display. But I just noticed that there's two white dots on the secondary display. When I turn on Mirroring, it goes away. However, the dots come back in the same spot when Mirroring is turned off. This happened in Panther, and while the problem went away after I did a clean install of Tiger. It's now back.
Does anyone know what would be causing this?