I don't know if it's the idea or not finished feature, but weapon damage won't go up with it upgrade. stats are important but not for weapon damage classes such as Warrior / DK / Hunters.
After you train another weapon skill you don't get it level 400 you should lvl up it by yourself, that kinda annoying .
If you have 2 weapons with same name, and equip one to special slot, you upgrade both at once.
heal mercenary don't have cd on spells or mana cost at tall. so i can spam all the spells as much as i wan't + holy shock is instant cast, no gcd, no cd no mana cost, think of it, how it's op :D
Quest http://www.wowhead.com/quest=14102/mistcaller-yngvar won't work, cause when you use http://www.wowhead.com/item=47009/mistcallers-charm the npc won't be summoned.