Normally an Arduino sketch merrily goes along doing what you want it to do, however sometimes you want things to happen at very specific time intervals. For example, counting the number of pulses over a set period of time to make a speedometer or frequency counter. In situations like these, the use of timer interrupts are very useful as you can stop the sketch at precise times and then call a specific action to occur.
Although it initially sounds complex, Amanda Ghassaei has written a detailed and easy to follow tutorial which explains the concepts of timer interrupts, followed by some great examples. So to get started, head over to the tutorial and get started. And we're on twitter and Google+, so follow us for news and product updates as well.