Brief summary of traits, those marked 'N/A' do not yet have implemented effects. This is confirmed by Ethrel on the forums. Probably will see more on traits in the 1.7 patch which is covering AI.
Hard worker: 1.25x work speed (all but removing stumps)
Lazy: Slower crafting speed than normal.
Strong Back: Can carry more weight without the reduction on speed
Weak Back: Haul less items in inventory before suffering speed decreases, greatly reduces movement speed the fuller the unit's inventory becomes
Bad Vision: -1 Line of sight radius, -8 levels on accuracy check
Good Vision: +0.5 Line of sight radius, +8 levels on accuracy check
Charismatic: Adds +5 to Trader level to maximum of 20. This means that a trader receives the benefits of 5 extra levels on top of their base level in the trader Profession. The 20 maximum means you will not gain any more advantage after level 15.
Courageous: 1.5x Attack Damage, if not Archer, Infantry, or Forager, guaranteed to fight
Disloyal: Higher chance of leaving town at low morale (This trait currently has no effect as morale was replaced with courage)
Over-eater: +2 food eaten every 2-4 hours
Clumsy: +0.2% chance to break tools/weapons, +20% chance to fall off ladder
Quick Learner: 1.25x EXP gain
Cowardly: If not Archer, Infantry, or Forager, guaranteed to flee from enemies
Athletic: Faster movement speed
Sluggish: Slower movement speed