Necessary second part to the previous post on how to make gold, what do you actually do with it once you got it? I already feel rich owning over 20k gold distributed over all my characters, and some traders report making 20k gold *per week*! What do you do with all of that virtual money, assuming you're not selling it for real world cash? Lets look at some categories again!
One category is operating costs. All the costs that accumulate while playing: repairs, consumables, flight costs, training costs, etc. These costs used to be high, especially for raiders, in WoW 1.0 and 2.0. But the game has changed since. Not only is raiding easier now, thus less wipes and less repair costs. But also the mobs in the raid dungeon drop more loot and cash. And the rules for consumables have changed, you can use less of them nowadays, so you spend less money on them. You can do a 4-hour raid on just 2 flasks and a stack of mana potions, and end up with more gold looted from trash and bosses than the consumables and repairs cost you. And even if you just do a handful of daily quests every day for reputation, the earned gold from that easily pays for all of your other expenses, like flight costs and so on.
The second category is bought gear, epics for your main or lower-level twink gear. There are a few world drop epics that are quite expensive, going for several thousand gold. I just bought some nice tanking shoulders for my warrior, because Auctioneer told me they usually sold for over 4k, and the seller had put them up for 3k bid, 5k buyout, and I noticed them when the timer on the auction was already running low. So 3k is currently my record for the most expensive epic I ever bought. But if you search your AH for level 80 epics, you'll find tons of them for around 1k, which is "affordable" if you spend some of your time in game trying to earn gold. Those affordable epics come from crafting. There are a lot of crafters out there, and they are all creating the same materials from recipes with long cooldown: Titansteel, Ebonweave, Spellweave, Moonshroud, Dragon's Eyes, etc. And the only thing you can do with those materials is make epics, which for a crafter is often the preferable path, as the AH is already flooded with those materials and prices are dropping. Plus making epics can get you those last skill points to 450. It doesn't cost you 1k gold to make lets say a Moonshroud Robe, it just costs you 16 days of cooldowns plus a few hundred gold for other materials. The other factor keeping the prices for epics down is again easier raiding. A crafted epic is of similar quality as the epics you can get in Naxxramas-10. If crafted epics were a lot more expensive, people just would decide it was less effort to go on a pickup raid. On the other side the prices for those crafted epics aren't sinking further, because more and more pickup groups for heroics don't even invite people any more if they don't have the kind of stats that those epics give. If you get kicked out of a heroic PuG for having less than 1700 spellpower, you'll be stuck if you don't buy those epics (vicious circle: can't loot epics without raids/heroics, can't get into a raid/heroic group without epics).
The third category is mounts and other vanity items. If you already bought your epic flying mount in TBC, you'll find that there isn't really any must-have mount to buy in WotLK, except for the affordable 1k gold for cold weather flying. There is no even faster flying (or teleporting, as I suggested for the Freezing Jihad) mount to buy for even more money as the epic flyer. What you can do is buy a tundra mammoth or hogger for nearly 20K. And those don't even fly! They are just as fast as the epic ground mount you could already buy in classic WoW. The hogger has one space for a passenger, and the tundra mammoth has two spaces. As added luxury the spaces on the tundra mammoth are taken up by a vendor and repair guy, which you can kick out if you want to transport other players instead. But how often do you really have to transport another player on a ground mount? Except if you dual-box and have an alt under level 60, the use of multi-seat mounts appears to be limited. Both the hogger and the tundra mammoth are more status symbols (Look at how much gold I can waste!) than really useful. And there are other mounts that are cheaper, more useful, and more impressive, like the various drakes you can get as drops or for exalted reputations.
Personally, as I'm not a big fan of conspicous consumption and status symbols, I don't really know what I'm making all that gold for. So I'm using it to finance high risk gambles on the AH (made 8 Darkmoon Cards of the North last night and lost, that is didn't get a single nobles card). Or buy expensive world-drop epics and twink gear for my alts. For me there is a certain fun in the act of making virtual money, I don't necessarily do it just to be able to afford something. And while it could be argued that making gold is too easy in WoW nowadays, on the positive side I'm pretty certain that the gold farmers are suffering. If you can make thousands of gold without too much of a grind, why would you want to buy that gold from a RMT company? So I'm wondering if the current situation isn't planned by Blizzard, as other ways to eliminate RMT have failed.