I started playing World of Warcraft around patch 2.1 of Burning Crusade with a Blood Elf warlock. Super impressed with the Blood Elf area, joined a leveling guild, guild imploded around when I hit level 40 in the Hinterlands, and I lost interest. Since I had already dropped the $60 on the original game and expansion, I decided to try and "get my money's worth" by rolling a draenei paladin on another server. I was immediately dismayed when I discovered that I could not, in fact, mail gold from my Horde toon to Alliance to help pay for my skills and upgrades. Hope waned...
...until I discovered the AH.
The metaphorical lightbulb lit up in two stages. The first stage was when I realize that even though X item would only sell for 50s apiece, 50s + 50s = 1g. The second lightbulb was when Lil Timmy's Peashooter dropped from a random mob in Hillsbrad. From my dabbling with BG PvP on the warlock, I knew that a market existed for items like this, and I was determined to find out the extent of the windfall that landed in my lap. This led me to Thottbot at the time, and eventually onward and upward to developing an instinct of slapping a price tag on everything that graced my bags.
The bulk of my fortune was acquired in two stages. The first stage was midway through TBC when I became the only seller of the Bold Living Ruby cut for TBC rare gems. Back in those ancient times, JC patterns were random world drops which led to cabals and monopolies; you would actually have players buying patterns they already had just to keep competition out of the market, and it typically worked. I spied the pattern on the AH for 500g (a fortune even back then) and basically had a license to print gold - I was making anywhere between a 50g to 75g margin on each and every Bold cut. I used to advertise in Trade as a sort of public service as well, but got burned pretty badly when I gave a raider a deal on doing 10 Bold cuts which he then tossed on the AH, undercutting the gems I already had on there.
The second part of my fortune occurred towards the beginning of ToC. You may or may not have known about Freya's room in Ulduar, but it was the one location outside of Wintergrasp that actually had Frost Lotus spawns as actual plants... that regenerated every 30 minutes (aka soft reset). I parked my shaman in there, chain-extended the lockout, and herbed anywhere between 5 and 14 Frost Lotus in an 5 minute run around the room, once every half hour. Back when Frost Lotus was selling for 50g apiece. God those were the days...
Currently I have eight characters level 80 or higher, including a level 72 hunter I am leveling to 75 just for profession purposes. Every single profession is covered, although I have four Engineers simply because I enjoy those perks in BGs the most. Every class is represented aside from druid, which will be (eventually) rectified once I get bored enough to start leveling the Worgen druid.