Exchange Server 2007 and leap year day Feb 29 2008...
Most of you might have received the following error:
"The Exchange server address list service failed to respond. This could be because of an address list or email address policy configuration error."
The research made by the MSExchangeTeam was that only occured if the System Attendant was restarted between 12:00AM, Feb 29 and 12:00AM, March 01.
Read more at source: http://msexchangeteam.com/archive/2008/02/29/448282.aspx