I suddenly, and unexplainably couldn't get Activity Viewer to launch. It just popped into the dock and immediately faded away again. I tried the first 'obvious' solution and trashed to prefs. Nothing. I trashed them again and restarted the laptop. Nothing. I went to Disk Utility to Repair Permissions. I expected that as usual I would get a couple of files listed as needing a small permission fix. Instead, it changed permissions on about every single file and directory within my Application folder! I copied the log into a BBEdit text document and it 5.5MB of plain text!! What could POSSIBLY cause something like this to happen?!? It seems that most of the changes are from -rwxrwxrwx to -rw-rw-r--. I'm no UNIX geek but it seems that means something like all admin/users/groups had full read/write access to all my files, and now it's set to proper file permissions. Activity Viewer works now BTW.