Interrupts. A very useful tool for our Arduino-based projects, however often misunderstood and thus cause a lot of heartache and debugging time to be used. Furthermore there's internal and pin change interrupts, plus different Arduino boards have differences as well with regard to interrupts. So if you're interested in brushing up on interrupts and the differences between them, check out the short tutorial on the rcarduino website.
Duane has documented some interesting notes that will be useful either now or in the future - so click here to get started. And for more, we're on twitter and Google+, so follow us for news and product updates as well.