More on Excel

You may have recently read of an issue in Excel 2007 involving calculation of numbers around 65,535 where Excel 2007 would return a value of 100,000 instead of 65,535. Excel incorrectly displays the result of a calculation in 12 very specific cases. The key here is that the issue is actually not in the calculation itself (the result of the calculation stored in Excel’s memory is correct), but only in the result that is shown in the sheet.

You can get more detail on the problem here:
Microsoft Excel : Calculation Issue Update

Microsoft have just released an update for both Excel 2007 and Excel Services in Office SharePoint Server 2007 that fixes this problem.
Description of the Excel 2007 hotfix package: October 9, 2007
Excel Services in Office SharePoint Server 2007 hotfix package: October 9, 2007

For all the latest information on Excel and Excel Services make sure you regularly visit the Excel team blog:
Microsoft Excel Team Blog