Not sure if this has anything to do with Lion. Never had this issue before and have been running Lion since it's release. Today while trying to log into a user account from the lockscreen I noticed the background had changed to a black picture with dot kind of things on it and the mouse would not let me click on anything (cancel, change user, etc.) I had to do a hard restart to get everything back to normal and get logged in. Has anyone experienced this before? Any ideas?