Never mind the Millennium bug of yesteryear in the last few days some of you may have experienced the Leap Second problem. Web sites such as Reddit, Gawker, LinkedIn, Foursquare and Yelp crashed after a "leap second" was added to the universal clock in order to keep up with the Earth's rotation. The leap second is even being blamed for a Qantas system meltdown associated with their global reservation software Amadeus.
So the Leap Second you ask…according to Wikipedia a leap second is a one-second adjustment that is occasionally applied to Coordinated Universal Time (UTC) in order to keep its time of day close to the mean solar time. The last leap second was inserted a day ago, on June 30, 2012 at 23:59:60 UTC.
The Coordinated Universal Time standard uses the international system (SI) definition of the second based on atomic clocks. However, the duration of one mean solar day is slightly longer than 24 hours. The purpose of a leap second is to compensate for this drift, by scheduling days with 86399 SI seconds.
So, basically, slight fluctuations on the Earth's axis meant that some days ended up being longer than others meaning that in a few hundred years time we'd be eating lunch at midnight if the problem went unaddressed. The extra second pulls everything back into line.