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This has to be one of the coolest and simplest things in PHP.

http://www.sitecrafting.com/blog/php-growl/

// Setup
$growl = new Growl();
$growl->setAddress('127.0.0.1');
$growl->addNotification("Test");
$growl->register();

// Send Notification
$growl->notify("Test", "Test Alert", "The body of the test alert!");

This simple class allows you to send OS X growl notifications to any valid network address. Pretty cool. Within a few minutes, Jared and I were Growling at each other in PHP.