@bl4nk: good point... You can hook medipacks being picked up, but you can't hook the resupply cabinet being used, so I'm not sure how to do the latter (other than a continuous check). naris' code didn't do this either though did it?
@berni: It's not limited to TF2, the point is that TF2 doesn't send the damage done in the player_hurt event, like most other mods do. This stores their previous health so you can get the damage done.