When your list has many formulas, or if a cell in the list is changed
after an AutoFilter has been applied, the Status Bar may show "Filter
Mode" instead of a count of the visible records.

The following MSKB article has information:

The AutoFilter status bar displays the "Filter Mode" message in Excel
http://support.microsoft.com/default.aspx?id=213886

And there are a couple of workarounds he
http://www.contextures.com/xlautofilter02.html#Count


s2m via OfficeKB.com wrote:
If Tools Option is set to Calculation is set to Auto, the filter count does
not work.



--
Debra Dalgleish
Contextures
http://www.contextures.com/tiptech.html