Formula to count dates

[hcubed]

Hi I Need a formula that can count the following dates but not the double ups. So for example
there are 2 (17/2/2012) the formula should only count this as 1

17/02/2012
21/02/2012
17/02/2012
24/02/2012
22/02/2012
24/02/2012
23/02/2012
20/02/2012
23/02/2012
25/02/2012
22/02/2012
25/02/2012
25/02/2012
18/02/2012
25/02/2012
27/02/2012
27/02/2012
27/02/2012
6/03/2012
27/02/2012
20/02/2012
20/02/2012
25/02/2012
23/02/2012
20/02/2012
22/02/2012
23/02/2012
21/02/2012
29/02/2012
22/02/2012
18/02/2012
18/02/2012
1/03/2012
23/02/2012
2/03/2012

[daddylonglegs]

If data is in A2:A100 try this formula

=SUMPRODUCT((A2:A100<>"")/COUNTIF(A2:A100,A2:A100&""))