[curt.clifton]

To add to what Pierre said, if you install Growl on your Mac your can get alarms for OmniFocus events on the desktop. Because of how Growl works, you configure the Growl reminders by using the Growl preference pane in System Preferences. (Essentially, OF tells Growl about important events like "task available" or "task due". You tell Growl whether or not you want a reminder to display for these events.)