Four usually. To answer why more than 1 blade:
At work:
-Mini AFCK for general stuff
-Calypso Jr Ltwt. for the razor edge
-Military for tasks requiring a longer blade
-SAK Manager or Manager 2 for the small phillips, scissors, nail file, tweezers, and toothpick.
Off work:
-Calypso Jr Ltwt.
-Military because I like it so much
-SAK Manager (or Manager 2)
-Starmate for the thicker blade
sometimes add one or more of the following:
-Dyad Jr (Micarta) for the serrated edge and the more "civilized" blades.
-Rescue Jr. for the serrated blade, but I've never needed it.
-AFCK for another large blade
-SS Dragonfly if I need one that's flat
-Dozier Slim outdoorsman when I can hide it well. It's new.
-Camillus CQB1 outdoors because it's new too.