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It is always interesting to see "common" electronic components used in fun, novel ways. Often, these methods have been well-known for quite some time and may even be the premise behind dedicated, more expensive sensors. However, the methods have a tendency to become vogue every few years. The decision to use these "alternative" components can be boiled down to a few key factors: cost, space, novelty, and usually the most important, availability (it's a nice alternative when you don't have the dedicated sensor sitting on your desk). I'm going to discuss two examples -- using LEDs as touch sensors and diodes as temperature sensors.  Can you think of any others?

Lucky for me, I have at my disposal several 3D printing machines at Georgia Tech. There is a Dimension fusion deposition molding (FDM) machine as well as several stereolithography (SLA) machines. They are very handy, particularly for rapid prototyping.  However, there is a cadre of hardware hackers seeking to build an open-source FDM machine, dubbed the RepRap project.

Noise cancelling headphones aren't exactly a new technology; they were first developed/deployed in the 1980's by Dr. Bose of MIT (yes, the one that owns the audio company). The operation principle is really quite simple -- use constructive and destructive interference to basically turn all external noises into silence. This is the same thing that happens to all waves, whether electromagnetic, fluidic, or in this case acoustic. If you're really curious, you can learn more about it from HowStuffWorks.