Soul Essence

This drops in Karazhan and is used for soulcloth.

So far all I have seen that is made from soulcloth is very high arcane resist gear, so I guess that means we can expect Karazhan to be an arcane damage instance.

Everyone in the raid (Tailor or not) can loot this item from a corpse if it so happens to be there. We send all of ours to the guild bank, and disperse it appropriately for Tailors who wish to craft some of the high +arcane resist gear for themselves.

There is not much use other than The Curator which would require this amount of +arcane resist, but it makes the encounter easier if your raid has atleast some.

I can concur that it has the possibility of being heavy Arcane. The vendor outside sells (with appropriate faction lvl.) arcane resist enchants. I've killed up to the third boss thus far however and have seen no major uses of Arcane. Most likely its just a way for us to acquire Arcane resist in the future, in the same way as Heroic tokens are used to buy the Infernoweave sets for FR for each class. Making resistance sets easier to build for everyone. IMO a good idea on Blizzard's part.