SYMPTOM:
When an attribute is imported into Excel 2007, the values are imported as text, as shown in the following screen shot. The apostrophe in the cell formula indicates a text formatting:

CAUSE:
This is the default behavior in Strategy Office
ACTION:
To allow date elements to be imported with date format, enable the following check box in the Strategy Office Options under General > Grid > Formatting > Apply date/time cell formatting semantics to date/time values

Now the elements should return with date formatting:
