Wound threshold don't appear to be working.
Using 0.77.9 - I've tried with several different pcs/npcs and regardless of what their health level is at (tried 75%/50%/5%) there are no penalties (-1, -2, -3) to attacks, saving throws, AC, caster level or skill checks happening. Also, I'm not sure if it takes Feats into account like Endurance which adds a +1 to penalties, the optional feat Twist the Knife which adds +1 to attacks against grazed, wounded or critical enemies, or healing spells where an additional hit point is given at 6th level (and another 1hp every 6 levels after) against grazed or worse conditions.