Many of the google hits are related to ATI Radeon video cards. I know you have ATI video drivers (from your logs) but I can’t tell if your graphics are intergrated or you have a card installed.

Do you know if you have a video card and, if there is, how old it is?

EDIT: Appearently ATI GForce cards are also affected to some degree.

EDIT #2: Heres a link to the ATI support site reagrding display corruption, including lines, checkerboard patterns, flashing dots, giant triangles, etc

http://support.ati.com/ics/support/default.asp?deptID=894&task=knowledge&questionID=28026

I’m wondering how a giant triangle actually fits on the screen.