I think that the game should have a skill for hauling. There are several reasons for this. At the moment, haulers don't get better at anything at all; this isn't very realistic (real-world haulers get tougher, and do learn how to handle large objects better.) It also makes it harder to keep dedicated haulers, since they won't be good at anything and will never gain stats.
This despite the fact that hauling is, in fact, one of the most important and common jobs in the fortress; to a great extent, a fortress' productivity is dependant on how quickly it can move things around.
What would a hauling skill do? It would lower the effective weight of carried and hauled items, effectively raising the dwarf's speed while hauling heavy objects. It would be trained by walking around while carrying enough to slow you down (the more you're slowed by, the faster you learn), so dwarves with heavy artifacts would rapidly gain the skill and strength necessary to carry them.
Thematically, it represents skill at knowing where to hold things, knowing how to stack them, how to lift and maneuver them through tight areas quickly, and so on.
It would also be a good skill for adventurer mode, of course. What adventurer doesn't want to learn how to manage carrying more things?