I've had this idea in my head for almost a year now. I knew what I wanted to do, but wasn't sure if it would work. After a long time of armchair-engineering, I decided that the best way to test my idea was with a soldering iron and a screwdriver.
Guess you're wondering how it was done.
I used an Arduino and a cheap remote-controlled outlet I found for about $15. I disassembled the remote control and connected it to the Arduino. If you want to try something similar yourself, never NEVER ever mess with the part that is connected to the power outlet. High voltage is not something you want to play with.
Anyway... the redstone lamp in the game is connected to command blocks that write to the server-log when activated. On the computer where the server is running, there is a small script that checks the logfile for the on/off events, and when it see one, it will send a message to the Arduino. The Arduino will then parse that message and send signals, emulating a button press, to the remote which will turn the lamp on or off.
So what can it be used for? I have no idea. Maybe some kind of virtual reality home automation?