Author's note
This article is meant as a mostly non-scientific source of information about the leap second event in relation to running (maintaining) computer systems - personal computers, servers, network equipment or any other systems using some form of external time source. While I only managed to put this together just about a week before this year's event (2015), I thought it's still worth it as it is quite likely that this is not the last leap second event we are going to witness. If you're reading this before this year's event, consider it a good refresher. If you're reading this before this year's event and it's all new to you, you may be slightly worried. There is still some time.
I think it's worth adding that I was tired of reading oversimplified statements like "every now and then the day becomes longer by a second" being the only meaningful fact conveyed in a two-page long blob of text. I wanted to provide something in the middle. I probably failed (in favour of too detailed), but at least one cannot say I didn't try. As you will find, the style this is written in, is an annoying combination of technical details interleaved with absolute basics. This text also is not a ready-to-eat HOWTO. If you're looking for information on how to configure your NTP or PTP, this is not the right place - but keep checking the site for more articles. This is a knowledge transfer dump about all things leap second. Perhaps an infographic or a leap second timeline could be added at some point.
There are no graphics throughout, so I'll start with a picture. Here is the Leap Second 2015 in stereotypes:
