We are using the wounds/vitality system from Unearthed Arcana, with modifications.

Characters who take damage lose vitality points first, unless the damage would unquestionably physically harm them—falling damage, attacked while flat-footed or impeded (held, tied up, etc.), critical hits, etc. Character who have no remaining vitality points begin taking wound damage. The idea is that during a fight, if you are "hit" you need to exert an extra effort to avoid being harmed, hence the loss of vitality. Once you are too tired to defend yourself (i.e., out of vitality points), you begin getting hurt in earnest.

Vitality: Vitality points (vp) are equal to constitution score plus maximized hit dice. For example, a sixth level rogue with a Con of 14 normally gets d8s in Pathfinder, so would have 14+6*8=62vp. The "Vital" feat grants +1vp per character level, and can only be taken once. The "Extra Vital" feat grants a fixed +4vp, and can be taken as any times as desired.

Wounds: Wound points (wp) are equal to constitution score plus character level. The "Tough" feat grants +3wp, and can only be taken once. The "Extra Tough" feat grants +1wp, and can be taken as many times as desired.

Dying: Dropping to 0wp or below means you are "dying" (and unconscious). Dying characters lose 1wp per round until stabilized, and have a 10% chance of stabilization as per normal D&D rules.

Death's door: Dropping to a negative wound value equal to your maximum wound points (known as your death threshold) puts you at death's door. While in this state, you continue to lose 1wp per round until stabilized, and must make a Fortitude save DC 15 + number of wp below your death threshold, or die. Even if healed, a character who was at death's door remains unconscious for at least 10 minutes, depending on the extent of injury. The GMs reserve the right to declare a character dead from massive damage (disintegrate, consumed by lava, head squashed in a trash compactor, etc.) where appropriate.

Death and the mercurial cosmos: If you die, another version of you could potentially appear later, depending on how "likely" your death was. So in that way, death is not as fatal as in normal D&D. :-)

Flat-footed: A flat-footed character lacks the presence of mind to apply his normal dodgery skills. Unless you have a power that states otherwise (e.g., Uncanny Dodge), you lose your Dexterity bonus to AC while flat-footed. In addition, when you are flat-footed (regardless of whether you somehow manage to retain your Dexterity bonus), damage dealt to you goes straight to wounds.

Impeded: An impeded character is physically restrained from avoiding attacks. Unless you have a power that states otherwise (e.g., freedom of movement), you lose your Dexterity bonus to AC while impeded. In addition, when you are impeded (regardless of whether you somehow manage to retain your Dexterity bonus), damage dealt to you goes straight to wounds.

Stun vs. daze: Any time the "stun" status appears, instead treat it as dazed. A dazed character loses their actions for the round, but does not lose their Dexterity bonus to AC, and is not considered flat-footed or impeded.

Critical hits: Weapons retain their normal critical range and multiplier, dealing extra vitality damage on a successful crit. However, a confirmed natural 20 critical deals 1X damage to wounds. For example, a fighter attacks with a scythe. The fighter normally does 2d4+9 damage with the scythe, but on a natural 20 crit instead deals 2d4+9 damage directly to wounds, and an another 6d4+27 damage to vitality, due to the scythe's x4 multiplier.

Critical hits versus a target already taking wound damage for some other reason (such as being flat-footed) take the fully multiplied damage to wounds (and the target is very likely hosed).

Nonlethal damage: Nonlethal damage (see Pathfinder p. 143) dealt as vitality damage depletes vitality as normal (i.e., the fact that it is nonlethal damage makes no difference). However, nonlethal damage applied to wounds is tracked separately. Compare the accumulated nonlethal damage to your current wound points to determine whether you become staggered or unconscious, as described in the Pathfinder book.

Temporary vitality: Treat temporary hit points as temporary vitality that is lost first when you take vitality damage. This temporary vitality cannot be used to fuel spells or other special abilities, but does serve as an extra buffer between you and the grim reaper.

Weapons with special properties: When a magic weapon with a special property such as burst or shocking deals damage to wounds, the special property's extra damage applies to wounds as well. So these types of weapons are fairly common for assassins and such to have.

Fast healing and regeneration: These special qualities differ from the normal wounds/vitality system. In our system, they affect wounds only, and you regain one wound point per round regardless of the fast healing or regeneration value. If you have regeneration, you can only be killed by your regeneration's weaknesses—e.g., trolls must be killed with acid or fire, but can be beat down by anything.

First round of combat: Unlike normal Pathfinder, we are waiving the flat-footed status from the first round of combat. You are only considered flat-footed during an enemy's surprise round, not before your first action on the first round.

Invisibility: Invisibility, by itself, does not cause an opponent to be flat-footed. However, it is a great aid when making stealth checks, which can result in an (and thus flat-footed) opponent. You always count as invisible to a blinded foe—but again, the foe is not considered flat-footed unless he is completely unaware of your presence (i.e., not in combat).

Sneak attack: You can use sneak attack whenever your target is denied its Dexterity bonus to AC. However, you only deal the extra sneak attack damage to wounds if you are already dealing damage to wounds for some other reason (e.g., the opponent is flat-footed or impeded, such as during a surprise round).

Flanking: While flanking, you may be eligible to deal Sneak Attack damage. However, since your opponent is not flat-footed or impeded with respect to you, the damage normally applies to vitality, not wounds.

Feinting: A successful feint causes your opponent to be denied his Dexterity bonus to AC versus your next qualifying attack. However, the opponent does not count as flat-footed or impeded, so the feint does not cause your attack to deal wound damage.

Hiding: If you are attacking an unaware opponent from a hidden position, the opponent counts as flat-footed versus your attacks during that turn. However, your position is exposed unless you successfully snipe with a ranged attack (see "Sniping" under the Stealth skill on p. 73).

Pinned: A pinned opponent counts as impeded rather than flat-footed (but the end result is generally the same).

Barbarians and monks: Barbarians use vitality to fuel their rage abilities; monks use it to fuel ki-based powers. More details later.

Intent in rules design: It is intended that Vitality recovery be limited to one point per round, two with the runemage and bard class feature linked to their Spellpool vitality.  The only exception to this is the Revitalize power, which is a feature of the Paladin, Geomancer, Cleric and Druid classes.  This power enables the user of the power to transfer Vitality into the subject on a one for one basis.  This can allow a party to make better use of the group's Vitality, however at most the party as a whole is regaining one point of Vitality per person per round (again, the runemage and bard exception being noted).

Anything that might be perceived to disrupt the balance of vitality regeneration will not do so.  This includes Fast Healing, Regeneration, healing magic, Vitality-Regen Cola, or The Thing You Found In That One Book.  That is all.  Please drive through.