Our friends over in the SBS world blogged this yesterday which I thought was one of the better discussions of the impacts:
The U.S. Energy Policy Act of 2005, passed by the U.S. Congress July, 2005, extended Daylight Saving Time (DST) in the U.S. by approximately four weeks. As a result, beginning in 2007, DST will start three weeks earlier on March 11, 2007, and end one week later on November 4, 2007, resulting in a new DST period that is four weeks longer than previously observed. These four weeks are referred to in this article as the “extended DST period”.
Unless certain updates are applied to your computer, it is possible that the time zone settings for your computer’s system clock may be incorrect during this four week period. This depends on where you live and which time zone you have selected.
Microsoft Daylight Saving Time Help and Support Center