- Fighters would gain it for defeating creatures that stood in the way of solving the quest, through strength of arms.
- Thieves for picking locks, climbing walls and using any other abilities to overcome obstacles that stand in the way of completing quests, or for sneaking past enemies so they do not need to be fought.
- Clerics would gain for using magic to aid the party and for turning undead.
- Mages would gain them for using their magic to overcome obstacles and enemies.
There would certainly be less fighting as fighting by itself wouldn't net a specific reward, except to the fighter - and even then only for defeating enemies that were part of the quest at hand. Thieves could gain the same experience for using their sneaking and hiding skills to avoid that same fight, or for backstabbing. Clerics and mages would only gain if they used their skills in the same combat to overcome enemies; e.g. turning undead, cause light wounds, magic missile, etc. But overall, I think it would de-emphasise combat as a means of advancement for non combat focussed classes and let them concentrate instead on what they are good at. What do you think?