The last time a leap second was added, it caused issues with a number of servers running Linux due to a livelock. [0] This had an effect on EC2 [1] and apparently other pieces of software [2] as well.

Nice to see Amazon being proactive about the forthcoming change. Time is just a prime example of one of those things that seems superficially simple, but turns out to be deviously complicated. (If you ever want to bore non-technical types to death at a party, just start talking about the history of time. Bonus points for mentioning the proleptic Gregorian calendar in context.)

0. http://serverfault.com/questions/403732/anyone-else-experien...

1. http://www.techspot.com/news/49229-leap-second-bug-amazon-ec...

2. http://www.wired.com/2012/07/leap-second-bug-wreaks-havoc-wi...