The buzzword in Excel 2003 is XML, best illustrated by the new mapping feature. This lets you map cells, columns and ranges to data held in XML data sources, so you can create Excel workbooks showing data from Web Services or other back-end data stores. The XML data is validated on input into Excel against a custom XML Schema under your control.

Excel can also save your work in a native XML workbook format, which keeps any formatting but avoids the proprietary XLS file format. You may also, however, save data as a pure XML data file, leaving any formatting in the template. This XML data file can be put through BizTalk or imported into a back-end database.
 
The other major change is the ability to define a range of cells as a list. This range can have its own 'total row' showing totals, averages and so on, plus a 'data entry row', where the range expands as new entries are typed in.

These lists may be imported or exported, shared with a SharePoint Website and updated through SharePoint or Excel via a live link.