Most killing moves in real unarmed combat are to the head, neck, or throat. But it would be cool if the different hits for say - back of the head, or temple strike, or neck punch would be differentiated in combat.
Also its mostly guaranteed once someone is disabled through usually non-lethal strikes to stuff like the solar plexus their going to either get their neck broken, choked out, or curb stomped. Bleed outs from liver or kidney hemorrhages can happen but not as often, especially with untrained brawling. Also groin shots can be lethal too, it would be funny if that were possible in DF. I see dwarves as expert brawlers, but not anything flashy. No tai-chi, fancy street fighter dancing, or taekwondo. But I do see them fighting like Russian martial artists, or Isreali krav maga as a base for dwarven martial arts. Maybe mix in some dwarvenly WWF, like throws that can crush spines (not sure if this can happen, I know teeth and toes can be grappled and ripped off).
Its been brought up in another thread, but unarmed combat involves allot more then just punches, in fact punching is not usually the most effective or safe use of your body to deal killing blows.
Furthermore it would be neat if different civilizations had different fighting styles... elves could sit on the ground with their hands clasped over their heads, humans could be boxers, kickers, orcs (if they were modded in) could do some form of Okinawan karate... goblins could use dirty fighting, like throwing sand and trying to gouge out eyes.
By no means do I expect all that to be put in or modded in, its all just a nice what if. Heck you could make a rogue-like based entirely off unarmed fighting styles from around the world, and fantasy/fiction.