The status quo for enchanting has been pretty constant for many years. There's dust. There's essence, usually three lessers equating to one greater. There are rare shards which may or may not have a lesser version and there is an epic crystal. That's what we've had for a very long time. Dust is dust, essence are essence, shards are shards, right?
Not anymore. Mists of Pandaria brought a fundamental change to the way enchanting materials work. Dust is no longer just dust, that dust can be traded up the chain all the way to a Sha Crystal if you have the desire. Likewise a Sha Crystal can be traded down the line all the way into dust.
This change hasn't sunk in with many enchanters, though, and my server's rife with gold-making opportunities because of it.
If I buy Spirit Dust right now it will cost me 5g90s to craft one Mysterious Essence which I can turn around and sell for 21g, essentially quadrupling my gold with a single craft.
When trading up:
5 Spirit Dust = 1 Mysterious Essence
5 Mysterious Essence = 1 Ethereal Shard
5 Ethereal Shard = 1 Sha Crystal (1 Day CD)
When trading down:
1 Sha Crystal = 2 Ethereal Shards
1 Ethereal Shard = 3 Mysterious Essence
1 Mysterious Essence = 3 Spirit Dust
Keep this in mind for selling mats at their most valuable stage and to be sure you pay the least for your crafting materials!