Hi all,
Having had similar problems, I've had a reply from Google Sketchup...
For me its my particular video card (ATI Mobility Radeon 9700) that simply can't stand having Hardware Acceleration turned on under SU6. It worked perfectly well with SU5... weird.
See this thread:
http://groups.google.com/group/Sketchup-Pro/browse_thread/thread/7aa2a4dd5ef40190#17aa3783531eb585