Interesting, and it makes me question what I thought I knew. But if your analogy is correct, Gargleblaster, a bullet fired in a westerly direction in the northern hemishphere would deflect to the south as well, ie to the left. But this is the opposite of how the coriolis force works.
While I think about it I have grabbed a bit of Wiki that seems to support the idea that coriolis acceleration depends on the direction of movement:
In non-vector terms: at a given rate of rotation of the observer, the magnitude of the Coriolis acceleration of the object is proportional to the velocity of the object and also to the sine of the angle between the direction of movement of the object and the axis of rotation.
https://en.wikipedia.org/wiki/Coriolis_force (the 'formula' section)