This year in the US, daylight savings time will start 3 weeks earlier than normal. This will throw off several applications that use time syncing. Exchange and Outlook appointments may also be affected by this change. Microsoft has released a document on how to address the daylight saving time change at http://support.microsoft.com/kb/931667/
Microsoft has also released a tool called TZmove on Feb 19, 2007 to adjust single Outlook account appointments to be adjusted properly. This utility can be found at:
I highly reccomend that you read the information at all of the above two links prior to using the utility.
Check my previos post at http://kenzig.blogspot.com/2007/02/exchange-2003-dst-critical-update-for.html for info on updating your Exchange server for the time change.