I'm also experiencing this problem on Gutsy RC. I did not have this problem on Feisty, and nothing in my computer specs has changed.
Mobo: Asus Crosshair
CPU: AMD64x2 6000+
Video: EVGA GeForce 8800GTS (640MB)
RAM: 2GB XMS2 DDR2-800
Monitor: Dell Trinitron (Could not find model number)
Is it just me, or does it seem everyone here having this problem is running a 8800GTS? Possibly an nvidia driver incompatibility issue?
I really hope this is fixed before final release.