I've tried the Disenchanting route myself, and began to make a hefty bit of cash, however I noticed that with my server's economy, the dusts were in general offsetting my profit margins negatively. In addition, I had to keep track of hundreds of transactions, remember what I bought the item for so I would sell the disenchanted mats at a resonable markup.
Right now I have a lvl36 Hunter with Mining and Skinning that feeds a bank alt materials to post on the AH. I have about 250G on my bank alt, which I think is a comfortable ammount for my level. I really only have to spend half an hour a day on my bank alt in order to collect all my mail and post all my auctions.
On my old server, my lvl57 Warrior had switched from double gathering to herbalism and alchemy after lvl40. While grinding up to lvl40 he had skinning and mining, and mannaged to farm up enough mats to sell on the AH and earn enough gold to buy his mount (back when the mount was the high ticket item), his riding training, his lvl40 training, and a full set of plate.
A little bit after hitting lvl40, as i mentioned earlier, he switched to herbalism and alchemy, ground them up to 300 in conjunction with his fishing skill. He was making a substantial ammount of gold fishing up stonescales, and converting them to oils and selling them on the AH. Eventually he also started to transmute arcanite bars, despite the slow proc times, and sell on the AH for a fair markup versus the price of the thorium bars and arcane crystals that he needed for mats. Unfortunately a guildmate needed arcanite bars for a quest, and I offered to help him reach his goal.
I think that as Mike said earlier, any trade skill can make you a heap of money if you find a niche and stick with it as long as you can make money with it. I do however believe that double gathering coupled with fishing is by far the best way of making gold, because there is no startup capitol to invest in order to produce your wares. Granted Disenchanting can make you alot of gold, probably the most out of any other profession, however if the market shifts too drastically, you're out your startup capitol until the market swings back into your favor.
People will underbid you, others will underbid them, and yet others will underbid them until there's no point in selling them on the AH until everyone else thinks so too and stops posting their auctions. Eventually the price will stabalize only to continue through the cycle again. My bank alt doesn't have the capacity to hold his stock of mats while still recieving goods from the main in the mail.