I am currently using 4 usbs on my Windows computer and 4 usbs on my Mac (so 8 in total)
2 for my wireless mice (1 per computer), 1 for my joystick, 1 for my headset, 1 for my pen and tablet for drawing, 1 for my pen storage, 1 for my iphone, 1 for my iPad/Keyboard holder.
And yes, I am using them all at the moment X_X