Similar to Mike, I was able to scream (not whistle: scream) a 300 baud carrier tone. This skill proved useful when I was in college and the mainframe system was down. Instead of sitting around waiting for the system to come back, I just went about my regular business around campus. Every so often, I would go to a nearby campus phone (like a free public phone but it can only make calls to other locations on campus), dial the 300 baud dial-up number, and scream the carrier tone. If I got a response, that meant that the mainframe was back online and I should wrap up what I was doing and head back to the lab.
Mind you, this skill isn't very useful nowadays.
What stupid computer talent do you have?