A Date Bug
Excel incorrectly assumes that the year 1900 was a leap year. This means Excel's internal date system believes there was a 29 Feb 1900, when there wasn't! The most surprising part is that Microsoft did this intentionally, or so they say! More information is available at http://support.microsoft.com/default.aspx?scid=kb;EN-US;q181370.
Here are some additional good links to information on dates and times:
HOW TO: Use Dates and Times in Excel 2000
http://support.microsoft.com/default.aspx?scid=kb;en-us;Q214094#6
Text or Number Converted to Unintended Number Format
http://support.microsoft.com/default.aspx?scid=kb;en-us;Q214233
Maximum Times in Microsoft Excel
http://support.microsoft.com/default.aspx?scid=kb;en-us;Q214386
Dates and Times Displayed as Serial Numbers When Viewing Formulas
http://support.microsoft.com/default.aspx?scid=kb;en-us;Q241072
Controlling and Understanding Settings in the Format Cells Dialog Box
http://support.microsoft.com/default.aspx?scid=kb;en-us;Q264372
How to Use Dates and Times in Microsoft Excel
http://support.microsoft.com/default.aspx?scid=kb;en-us;214094
Dates and times are probably one of the most confusing areas within Excel. Armed with this information, hopefully you will understand more about their many quirks and have an easier time dealing with them.
