I just upgraded to 11.04 and have been having this issue. I'm using the Unity interface, my card is an Intel GM965.
When I close my laptop lid I have it set to just blank screen. When I open the lid again, the mouse moves but nothing is responsive. I can switch to a terminal but when I switch back, the terminal text remains there with just the mouse moving again. I have to do a gdm restart to get Unity back.