We keep a few (6-8) in the bank for people to enchant 372 items with the best enchants, and provide for free half the crystals for those enchants. Excess crystals we sell on the AH for gbank money. Guild didn't form until near the end of WotLK but we've managed to make about 400k from BoEs and Crystals so far this expansion and hope to use that gold in 4.2 for whatever the new crafting item is.