If I'm late, you'll know why...

Leap Seconds: "The Earth is constantly undergoing a deceleration caused by the braking action of the tides."

Though it turns out that this deceleration is probably unnoticeable to all but the most astute observer:

Through the use of ancient observations of eclipses, it is possible to determine the average deceleration of the Earth to be roughly 1.4 milliseconds per day per century. This deceleration causes the Earth's rotational time to slow with respect to the atomic clock time.

The fascinating facts continue:

The length of the mean solar day has increased by roughly 2 milliseconds since it was exactly 86,400 seconds of atomic time about 1.79 centuries ago (i.e. the 179 year difference between 1999 and 1820). That is, the length of the mean solar day is at present about 86,400.002 seconds instead of exactly 86,400 seconds. Over the course of one year, the difference accumulates to almost one second, which is compensated by the insertion of a leap second into the scale of UTC with a current regularity of a little less than once per year. Other factors also affect the Earth, some in unpredictable ways, so that it is necessary to monitor the Earth's rotation continuously.

And one more slightly related item. Check out the title of the guy that authored this urgent government bulletin.

http://tycho.usno.navy.mil/leap.html

DENNIS D. McCARTHY
Director
Directorate of Time

And who would have thought there would be 43,000+ references to "Leap Second" from a Google Search.