Unique Count with Criteria

Hi,

Here is a link to a file that answers Chandoo's question.

vacation-calculations.xlsx

The formula in cell G19 is an example of how, given a data set with non-unique Identifiers, how to count the number of unique elements meeting a certain criteria.
In this example, we have a list of employee names and the dates when they took vacation and we want to know how many unique people took a vacation between two given dates.

Hope this helps.