You may have heard of the obsidian/saronite shuffle; Prospect stacks of ore; turn it into jewelery; disenchant and sell off essences and dusts? Skills used Mining; Jewelcrafting; Enchanting. (http://consortium.stormspire.net/content/183-shuffling-spreadsheet-killed-them-all.html)
Or how about smelt stacks of obsidian and elementium ore; Create stormforged shoulders; disenchant and sell off the Heavenly shards? Skills used Mining; Blacksmith; Enchanting (http://wow.joystiq.com/2011/05/25/how-to-turn-ore-into-heavenly-shards/)
Generally these are profitable activities in their own right. (And no - I don't even have a tool capable of mining saronite ore; let alone obsidium; AH is where I farm). I have a problem with the default process; most authors encourage you to crush the majority of crafted items regardless of their relative value (with the possible exception of blue jewelery from the obsidian shuffle).
For the record; I am not doing a lot of ore shuffling, (I'm stretched to collect auction house mail some days), but somone I ran with wanted me to dump a bit of ore recently.
The stormforged shoulders disenchant to a single heavenly shard (~90g); a nice enough markup from the price I would have sold the underlying ore for. However, according to my auctioneer, the shoulders had a sale price about 250g. There were none on the auction house.
I crushed the majority of the shoulders, but kept a one for sale. It sold on the first post cycle. In the past, I have done the same thing with the various green quality jewelry from the ore shuffles; keep one or two; post the rest. They are not always quick sellers. If an item only has a slightly higher (theoretical) sale price I will crush it.
I keep one bank alt aside for selling trash. If I don't know what I want to do with something; off to my trash seller it goes. I also only infrequently log on to him. When I do; I sell stuff using auctioneer with add-hoc pricing. No camping; just set and forget.
Doing extra work to sell at 90g; when you could do less effort and sell for 250g; it just feels wrong.