Currently, We have to convert the Excel file to the CSV format before importing in the Moodle gradebook. It may be nice to directly allow to import in the Excel 2007 and 2003 format.
The new phpExcel lib implemented with
MDL-35356 for 2.5 will greatly help.
Just a note that the task
MDL-32259 is similar but has been considered duplicate of the MDL-35356.