My group has been expirimenting with two house rules the past 5 sessions and are greatly satisified with how each one balances the game and adds a bit more realism. In all honesty critizism is welcome, but unnessisary as we have all decided to keep these new rules, and I post them in the hopes that you may try them as well.
I don't know if anyone else has any special rules for actual damage done to the head, but my group just developed a new method of portraying how blows, slashs, stabs, shots, explosions, ect, are more lethal when dealt to the head. In our opinions the improved critical chart wasnt enough to satify how gruesome a well placed headshot, even with a mundane weapon like an arrow, should be shown.
So for all damage rolls to the head we grant a double damage rule. Whatever the damage after adding the bonuses is doubled, PCs can spend a fate point to relocate the shot to the body if they so choose. After playtesting the rule for 5 sessions we have all come to the conclusion that this A) makes called shots worth the negatives, and B) keeps us mortal.
How oftin are you playing in a group where everyone is running around with autoguns/ autopistols loaded with manstopper rounds. Its cheep, and lethal. But in my opinion the lethality of this tactic is based off the number of chances one gets with the Full Auto action. So in the group we are in we have started using the rule that all PCs must denominate which die will be their Righteous die. This is the only die that gets a chance at righteous fury. This rule extendes to Great Weapons, but not Tearing weapons. It has ran well.
Hope they help,