How to count the number of customers ordering at an item - pivot table

Hi,

Sample workbook would be helpful.

hmm ... why pivot ?

select A,count(B) from table group by A

oups : missed the excel part ;) sorry
if you need a formula for a specific product, something like this should do : count(if(A1:A100 = "myproduct",B1:B100))

you'd need to replace the "sum" by a "count" in the calculated data ( or add an extra column ).
click on the pivot and find where you can add a new "value" or "set of values" which will actually ask for the type of value ( sum, count, count unique ... ) and add the corresponding extra column.