I've been having random black screen freezes over the last month since updating to Lion. Lost much work and spent much time trying to determine the cause. This has been a high cost for my employer in terms of person hours and lost work. I also went to the Apple Store and their Genius could find no cause or solution. I have the flurry screensaver pop up over the login screen as well as these freezes. This thread describes exactly the same symptoms I've been having. I have a mid-2010 MacBook Pro.
I had been searching for "black screen freeze" postings and just today decided to search for "screensaver at login screen" and found this thread, which seems to have solved my problem. Too bad the Apple Genius didn't know about it.
I had AirDisplay installed, the latest version as of this writing. I removed AirDisplay using Uninstall Air Display.app. It's installed by AirDisplay in the Utilities folder, in case anyone else wants to find it. The flurry screensaver at login window issue is gone now, and I haven't seen any crashes since, though my fingers are still crossed.
Thank you for locating the AirParrot uninstaller. They buried it in the FAQs on their site. Your link is broken because it has spaces in the filename. This should work:
http://airparrot.com/download/AirParrotRemovalTool.zip
I have Air Parrot but haven't installed it yet. I certainly won't now unless they specifically state that the problem with our models has been solved. Even then probably not. My confidence has been shaken.
I'm going to give feedback to Apple and the makers of AirDisplay. One or the other or both should have an alert that pops up during installation warning users with our models of this issue. As I said, this has been very expensive for my employer, probably thousands of dollars worth of time wasted all in all. This is a very. serious. problem.