I've been invited by Markco to comment on his post Making Gold by Stockpiling Saronite for Cataclysm. I certainly appreciate the opportunity to participate in the discussion, however I'm not sure I agree with his logic on saronite ore for a few reasons.
First, I think anyone who plans to powerlevel a new profession in the first weeks of Cataclysm would be a fool not to stockpile materials now while they're bored. That's what I've spent the last month doing -- prepping for Cataclysm. So you have to eliminate people who plan ahead from your prospective buyer list.
Next, I think newly minted toons will usually take a gathering profession with their manufacturing skill. The primary reason to take two production professions is to min/max for raids and these toons won't be raiding anytime soon. Why torture yourself by passing up oodles of ore while you quest, just to pay outrageously for it later? I can't imagine many people choosing to do that.
That mainly leaves players who purposely take two manufacturing professions to fill holes in their tradeskill line-up. Players who plan to go dual-producer on their new toon probably already have a gatherer who can collect materials for them. As such they are unlikely to pay premium prices for ore they know they can collect themselves.
The only group left is people who are poor planners but still end up taking two manufacturing skills for some strange reason. Poor planners are notorious for having no money, this is a major symptom of a poor planner. The odds of them skilling up a new toon all the way to Northrend and still having the cash to pay through the nose for mats is slim. I would guess this type of player will either abandon the profession because they're broke and can't afford to keep buying mats, or will cave and level up the proper gathering skill. The way I see it, saronite is a gamble on people with poor planning skills and tons of cash. I wouldn't count on a large number of people fitting into that category.
Another thing to keep in mind is that lots of players will be leveling through all the old zones. A good number of them will take gathering skills and collect herbs/ore/skins while they quest through. Some of that material will end up on the Auction House. Things that look valuable to us today may not be the same when every zone that currently exists is swarming with new questers.
I remember in the early weeks of WotLK I had a friend who was skinning everything and getting a good number of arctic furs. I told him to hold onto them, that eventually it would be valuable because they were needed for high end craftables. All he could see was that for the first month people were selling them for nothing and he got disgusted. He continued to sell them for nothing and was bitter over the whole thing. Luckily for me, I was buying those firs for when my leatherworker was ready for epic recipes. The moral of the story is that items change in value based on availability and their current (not future) usefulness. Cataclysm will significantly change the availability for many items and I think it's a gamble to try and predict the resulting prices.
There are some things I think you can count on. Anything you can make that's required by another profession is probably a good bet. Armor and weapon vellums for enchanters would be a pretty solid choice. Honestly though, I'm not sure I'd pin my fortunes on tradeskills at all. For me it's a no brainer to follow the sure thing - levelers. The vast majority of people are probably going to roll a worgen or goblin. Those toons will need gear. It's pretty unlikely that they'll be able to stay kitted out for 58 levels just with quest rewards. I say to use all the recipes you've been collecting for 2-5 years to make those people stuff to wear! That should be a viable market for all types of players, not just the poor planners. It may not be as quick and easy as camping the auctions and reselling stuff you bought, but it's a great way to clean old mats out of your bank :)
My personal favorites for Cataclysm items are enchant scrolls (raid quality recipes from vanilla, BC and WotLK), flasks and jewelry. I think every leveling toon is going to want at least some enchants for their gear. And they'll probably be willing to spend a bit of money for buff items (potions or flasks) that help them kill foozles faster. I suspect that rings and necklaces will be in short supply based on traditional drop rates. Luckily crafted jewelry is well itemized compared to the old vanilla stuff, so JC items will probably be more appealing to buyers than loot drops.
I agree that eventually saronite will become valuable, as do all "old world" ores once their content is irrelevant. We see the evidence of it now with Vanilla and BC ore prices. If you're willing to hold onto saronite for a while, eventually you'll be able to sell it for a good price. Of course by then the bulk of the tradeskill leveling will be over as well. I would say enter this segment of the market at your own risk ;)