Passive Defense from Shields

[Varyon]

Spawned from a discussion in the GURPS Loadouts: Low Tech Armor thread, this is my take on making the shield a bit more realistic.

In the above thread, Dan noted that a shield makes the torso a rather unattractive hit location, while the current GURPS rules do just the opposite. The easiest way to address this would be to have a shield give a penalty to hit the torso, but it was brought up that doing so while having shields grant their DB to other defenses may be double dipping.

My solution is relatively simple - shields impose a penalty equal to 2xDB on attacks to the Torso (and the arm the shield is strapped to, at a minimum). Shields grant full DB as a bonus to any Block with that shield, but only half DB (round down) as a bonus to any other defense. If the penalty or bonus makes the difference in any attack or defense, the attack hits the shield.
These are true for any frontal attacks. Attacks from the Shield side are defended with full DB for any defense, attacks from the Weapon side need deal with only half effects (-DB to Torso attacks, half DB for Blocks, no DB for other defenses), and attacks from behind ignore shields.

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Another point brought up was how easy it is to target the arms/legs, and how difficult to target the head. In Pyramid #3.34, T-Bone suggests a Dodge bonus for attacks against extremities. I would extend this bonus to Parries against limbs as well, but with a success meaning you got your arm/leg out of the way (just as with a weapon). What skill to use is up to the GM - Brawling/Karate/etc is appropriate for both, weapon skills may be appropriate for the arms, and Acrobatics/Dancing/etc may be appropriate for the legs - particularly in cinematic games!
As for easier headshots, in that thread I recommended allowing a downward strike that basically worked out as +2 to attack, +1 to the target's Dodge, and hitting the torso on a miss by 1 (if the target has a shield, it may be appropriate to let the attacker make another attack roll, with the shield penalty, to see if he hits the torso or the shield (alternatively, just assume he hits the shield).
EDIT: The above is misleading. The +2 to attack is a relative +2 - you're still targeting the Skull at -7, for a total -5 to hit.

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Naturally, I'm interested in the ideas of others on both topics. Hopefully this thread will allow us to maintain this discussion while leaving the Loadouts thread for actually discussing that work.