Some time ago, I purchased this T-shirt from Think Geek and it was the hit of the company pot luck! I do believe however that I've been trumped... well done Chris Ball!
"How's it work?
There's a Python script (gmail.py) to be run on any Bluetooth-enabled
device with Python installed (I use an Android phone, you could use a
laptop). The script simply downloads your Gmail RSS feed to see how
much unread e-mail you have, and sends that number over a serial port
every two seconds. I use /dev/rfcomm0, which is the serial device that
connects my phone to the Bluetooth dongle on my Lilypad.
There's also a C program (lilypad.pde) that runs on the Lilypad, reads
a number over the serial port, and renders that number on a set of LEDs
(I use seven LEDs). That's it."