You would be damn surprised if you actually saw what many geeks of this world do in their spare time.
Staying on the Lego theme, a Lego Rubix Cube Solver
[youtube]eaRcWB3jwMo[/youtube]
A Rube Goldberg Machine that was created by the band and some engineers the video is for. (I recommend watching this one, it's very good)
[youtube]qybUFnY7Y8w[/youtube]