I just made a little fun thing out of my mailbox notifier.
It originally just played a sound, then continued to flash the LED.
Now it plays the tone, flashes the LED once, and then a push message to my iPhone is delivered.
More information here: http://bld.is-a-geek.com/2011/01/02/snail-mail-notifier/
Thats really cool, hate going out to an emty mailbox 
Pretty easy to make, would also be easy to use an Ethernet shield with the arduino, but I didn't have one, plus I already got an arduino talking to a computer over serial.
Also got two programs on my blog on how to do the serial communication, and how to do the communication with the prowl service to do the push messages.
That's great! 