Comment 7 for bug 772925

I found a recommendation to disable the "Sync to vblank" option, which seems to have solved the issue for me; I wrote about it, along with links to the information I'd found, at http://www.preshweb.co.uk/2011/05/ubuntu-11-04-x-freezing-after-screensaver-active-laptop-lid-closed/ - that may be of use to anyone else experiencing this issue.