You know, this is one of those things that I feel is better left abstract. For the most part, IMC hit point loss does equate to damage taken. But I don't have any exact measurement of what equals what, I'm usually just trying to add flavor to the combat.
"You manage to raise your staff to block the blow, but it hits you with sufficient force to get the wind knocked out of you."
"You see the hobgoblin taking careful aim and are shocked to suddenly see your shoulder sprout a crossbow bolt. You can't help but give a cry out in pain."
"The thief managed to dart around you, and you suddenly realize you're being attacked from both sides. You hold your own briefly, but he manages to hit you with a vicious stab to the leg."
"Despite your breastplate, when the ogre's viciously spiked club hits you in the midsection, you're pretty sure you felt a couple of ribs crack."
These wounds are almost always flesh wounds, but the descriptions give the better roleplayers in my group something to work off of. You'd be surprised how many players actually like the idea of emerging from a fight bruised, battered and bloody.
If a player gets a finishing kill, I usually invite them to describe what they do. If a player every gets knocked below minus ten, there's that dreadful sucking in of breath and glances traded around the table. It happens and so far no one's flipped off the handle, so I feel pretty safe after I've gauged the emotional reaction to describe what happened. This actually seems to be a little cathartic, both for me and the player, and gives the other player emotional reason to get even more engaged.