One of the worst-designed elements of BRP (which I otherwise consider an excellent system) is that it is a system with hit locations but with 7 of them. Hit locations are tremendous fun as they allow PCs to determine where specifically on a foe they have hit, but having 7, instead of 6 or 8, slows down gameplay. In Legend / Mongoose Runequest II, this is resolved by rolling on a d20 chart, which is too complex to be memorised easily. My personal preference is to merge the "abdomen" location with the "chest" location into a "torso" location and use a d6 to resolve it. I would use the following chart:
2: Right Arm
3: Left Arm
4: Right Leg
5: Left Leg
In Openquest, without locational HP, the main reason to use hit locations is just to add some concrete detail to the hit. I actually recommend against locational damage, as I find that it requires a complex chart that is a hassle to check in play, especially when players heal to full and must check each location's max HP on the chart to make sure they aren't shorting themselves or suddenly gaining HP.
Addendum 05/05/12: If one did want locational damage, I would add SIZ + CON + POW and divide it equally amongst the six locations (round up). Remainders go to the torso. This would give an average of 5 HP per section (other than the torso), which would make armour much more important.