I've just about wrapped up a marathon session of leveling via mining and herbing. I'm nearly level 85 on my druid, I've made 100,000 gold (yes, the comma is in the right spot) from about 25-30 hours of /played time since Cataclysm went live. I can't say it was particularly fun, though in a way it was good to build up a bankroll so that I don't really have to worry about gold again on my primary server.
I would suggest that if you want to cash in on some of the farming that still needs to be done, consider picking up Herbalism and Mining as a Profession pair (if you aren't already heavily invested in other professions). It took me about 3-4 hours of /played time to level herbalism from 1-525. Though this may seem fast, remember that 310% flying speed in the old-world zones makes leveling a gathering skill go very quickly. When you've got both working for you and when stacks of raw materials are selling for 200-600 gold, it doesn't take long for things to add up to a small fortune. Find a good Herbalism Guide or Mining Guide and reap some of the profits, but you have to act quickly. The opportunity to profiteer is gradually going to wither away.
If it is January of 2011 or later and you are reading this post, it probably doesn't make sense to make any exceptional effort to switch to a gathering profession. I doubt that stacks of Twilight Jasmine will be selling for 600 gold at that point. And I'd be surprised if they were even a third of that.
I've also managed to flip some items using Auctioneer. My big score so far was buying out all of the Heartblossom below 100 gold a stack soon after they announced the nerf to herb and mining node distribution in Deepholm. Given that Heartblossom only grows there, I (correctly) figured that it would quickly shoot up in value. I've already sold about half of the stacks at between 200 and 250 gold, so profit could end up being in the 10k-15k range just for using some common sense.
What I wish I'd followed through on is buying up all the Pyrite Ore that was priced below 250 gold a stack for the first three days. I kept saying to myself: this stuff is going to shoot up in value when players start to actually craft things with it. But for some reason I didn't pull the trigger, and overnight it shot up to 700-800 gold a stack.
I'm a bit surprised that Obsidium Ore is already looking to dip below 100g a stack. It was also surprising to see several players with 50-100 stacks of it on the Auction House. I wonder if the macro-farmers have started in force, especially given the choice of name that several used for their auction postings. Like I said, if you want to get on the money train (and level one of your high-level characters at the same time), you better get in on it now if you have an interest in farming ore and or herbs. With natural production of a gold-hungry player base plus the illicit production of the gold-selling player base, prices are probably at their peak a few days in and will decline gradually over the next few weeks to the point that only the real-money traders will be out doing the dirty work.