I just solved it for my 2010 MacBook Pro. I was researching an unrelated problem with 1Password locking all the time. And it turns out to be related.
AgileBits, makers of 1Password reports: "The general class of application that provides any kind of video drivers for screen sharing, supports remote devices or computers as “monitors”, etc. has been identified as needing to either be updated for Lion, or temporarily removed from your system if the software vendor hasn’t yet gotten a compatible update ready."
It appears to be the result of specific apps, including AirDisplay, LaunchBar, and DisplayPad. I was using AirDisplay.
I just uninstalled AirDisplay (via the uninstall script) and rebooted and the screensaver problem has completely been fixed. Thank goodness.