I bought . . . a lot of Eternal Shadow a few weeks ago. Between Ebonweave, Eternal Belt Buckles, Rituals of the New Moon, Titanium Plating, and Titansteel it is by far my most used Eternal. I bought about 1000 a few weeks ago for all of these purposes but over the past week or so the pre-Cataclysm buying has halted as everyone braces themselves for the end of the world as we know it.
So what do I do with the ~200 leftover Shadow when most of these items will be obsolete? Well, I'll give you a hint. It's crafted, I've already mentioned it, and RPers love it.
Very few of the people who purchase Rituals of the New Moon do it for the actual stats of the item, they do it because everyone likes turning into things and looking different from time to time. This won't change in Cataclysm. What will change is the supply of Eternal Shadow. Without everyone constantly running around Northrend eternals of all types will be much more scarce. This will effect other items which will still be desirable in Cataclysm, such as a Chopper/Hog, but I feel that the "little guys" like inscription books may be forgotten.
Rituals take 5 IotS, 10 Parchment, and 3 Eternal Shadow; when you create them you create a random colored wolf book: red, white, grey or black. Right now the parchment is actually a large chunk of the crafting cost due to cheap shadow and relatively cheap herbs. Well, when no one's farming Shadow and IotS has to be farmed or traded down for specifically you can bet that you'll see fewer Rituals on the AH/in trade. I'm stocking up even further on Eternal Shadow now while it's cheap; even if for some reason Rituals bottom out I can always funnel it into Titansteel => Choppers for all the people likely to have 12.5k gold that they'd never seen before.