I have a simple (really!) sheet that I created in the Numbers (part of the new iWork ’08). In this sheet, I created two tables and a text box.
When I exported this sheet to Excel and viewed the result from Excel, I was disappointed, but not surprised that the exported sheet looks horrible: each table is on a different sheet, even the text box gets its own sheet.
The lesson? If you want to create a spreadsheet using Numbers and later exported to Excel, keep it simple with one table. Or, you might want to export your sheet to PDF for read-only sharing.