Daylight Saving Time starts earlier this year. Any software, such as your operating system, that automatically does the "spring ahead, fall back" may not be able to handle the change. Microsoft has a February 2007 cumulative time zone update for Microsoft Windows that will make the adjustment. Follow the link to the patch for your version of Windows.
Microsoft has a Time Zone Data Update Tool for Microsoft Office Outlook that will configure Outlook for the changes in Daylight Savings Time. Read the extensive discussion of this tool, as well as some Windows Registry edits that need to be made.
If you apply the Time Zone Data Update Tool for Microsoft Office Outlook, it will not change any recurring calendar items in Outlook Web Access. Microsoft says that creators of those repeating items will have to manually update them.
If you maintain any Java applications that may be affected by the change in Daylight Savings Time in the US and Canada, Sun Microsystems has a paper discussing some of the ramifications. Read it here.
So for triggering these patches (and for making me revert to getting up in the morning in pitch darkness for another couple of weeks) the U.S. Congress wins their first Bug of the Month award.