Which, I think I've mentioned, is the coolest name for any organization ever.

To: authorities responsible for the measurement and distribution of time

A positive leap second will be introduced at the end of June 2012. The sequence of dates of the UTC second markers will be:

2012 June 30, 23h 59m 59s
2012 June 30, 23h 59m 60s
2012 July 1, 0h 0m 0s

The difference between UTC and the International Atomic Time TAI is:

from 2009 January 1, 0h UTC, to 2012 July 1 0h UTC : UTC-TAI = - 34s
from 2012 July 1, 0h UTC, until further notice : UTC-TAI = - 35s

This means that tomorrow, 4:59:59 PM PDT will be followed by 4:59:60 PM PDT prior to the advent of 5:00:00 PM PDT.

Of course there is a leapsecond.com:

Now that you know what a leap second is, have you wondered if you can see one? Can you hear a leap second? Several of us enjoy capturing leap seconds. You have to be quick; you have to plan ahead. You have only one second to fish and then wait a year or two, or even seven, before your next chance. Below are examples of catching a leap second in the act.

As a kid in the summer of 1972 I used a short-wave radio cassette audio tape recorder to record the first leap second. Alas, I still can't find that tape.

Also, great news, everybody! The venerable leap second has gotten a stay of execution until at least 2015: ITU Radiocommunication Assembly defers decision to eliminate the leap second. The Earth gently wobbles in relief.

Previously, previously, previously.