Have you ever been annoyed by the fact that you mounted the pcb and needed to update the firmware? Dismantle everything, connect to the programmer or just to the serial cable if you have bootloader installed already, not to mention if your hardware controls some power device like a motor, then you need to be careful not to fry your PC’s serial interface or the motherboard, the solution is simple and available, use a wireless connection.
The guys from Sparkfun made a robust and yet compact communication protocol which can be used via wireless link to download the firmware, they use the XBee module which is a Zigbee to serial converter, they mounted the XBee on to the usb to serial converter board and there you have it, simple and robust wireless link which can be used also for debug purposes. The bootloader is written in C, and the PC program in visual basic, the XBee modules can be replaced with any wireless solution, I will most certainly try it with some bluetooth modules.
Wireless bootloader for AVR: [Link]