I like some of the hints about the kinds of things that can tie in with 'bloodied' condition, both offensively and defensively.
For example:
per-encounter attacks which recharge when first bloodied (Yuan-ti Champion "sword and bite" attack, Harpy "lure" attack, Fire Archon "fireburst", Copper Dragon "Acid breath")
Werewolf champion "Bloodfury: +4 attack and +10 damage while bloodied"
Rage Drake "Bloodrage: +5 damage while bloodied"
"Bloodthirsty 10: +10 damage against bloodied targets"
Bar-Lgura "while bloodied this creature can push target 1 square on a successful attack"
per-encounter attacks which recharge when an adjacent enemy becomes bloodied (Osyluth/bone devil "reaping claws", which is a kind of 'flurry of attacks')
per-encounter abilities which trigger when a target becomes bloodied
Cliffwalk archer "Timely Shot: when an enemy becomes bloodied make an immediate missile attack against them"
per-encounter abilities which trigger when you become bloodied.
Cliffwalk archer "Blood Arrow: When an enemy melee attack causes you to become bloodied you get an immediate shift and missile attack back at that enemy."
I could imagine quite a few of these transferring across to 4e rules for monsters and/or character powers.
Cheers