Distinct Count:

=SUM(1/COUNTIF(A1:A9&B1:B9,A1:A9&B1:B9))

Example:
Flint Dianne
Jones Amber
Jackson Dorraine
Smith Laurel
Smith Lesley
Smith Lesley
Smith Lesley
Jones Amber
Jones Amber
=5

Ola Sandstrom

Note:
Confirm the formula by holding down Ctrl and Shift, and then press Enter.
Othervise the result will be 1.