I posted the source to Avviso, my Arduino and Processing libraries and examples for sending push notifications to your iOS device via Prowl. Avviso works best with an Arduino and Ethernet shield, but it can also work with a USB Arduino and the included Processing library. Apple's push notification service is fast, direct, and free. Consider using it in your Arduino project along with the traditional alternatives of email, Twitter, or SMS.
Thanks to Prowl for dropping the SSL requirement from its API in January 2011, which made it possible for the Arduino to communicate with the service directly. (Avviso with Processing on the PC still uses SSL, of course.)