How can I disable ALL notifications in OSX Lion?
First of all, let's make sure that we are talking about Mac OS X "Lion" which is version 10.7 and not "Mountain Lion" which is version 10.8. Is this correct? This is important since Notification Center debuted in 10.8.

If you are on 10.7 then I may suggest two workarounds.

1. You may want to install Growl app and set all notifications off. Please, read Help and Blog sections before purchasing the app.

2. You may want to upgrade to "Mountain Lion" and then turn off all notifications by entering this commands in terminal:

launchctl unload -w /System/Library/LaunchAgents/com.apple.notificationcenterui.plist
killall NotificationCenter


If you'll ever change your mind, you can then return it back by:

launchctl load -w /System/Library/LaunchAgents/com.apple.notificationcenterui.plist


Hope this helps.