When playing a lower level character in World of Warcraft, one thing that constantly surprises me is how separated the fixed, NPC-based economy has become from the variable, player-based economy. Looting a level 30ish mob gives my character around 1 silver worth of cash and vendor loot. But finding just one mining node, even copper, already nets me around 1 gold. And recently I was lucky to have a blue random world drop, Feet of the Lynx, a highly desirable twink item, and it sold for over 100 gold.
The reason for this disparity is the level-based inflation that all level-based games share. Basically the only real unit of currency in a MMORPG is time. Thus the amount of copper you can mine in one hour is "worth" 1 hour. And how much that corresponds to in gold depends on what the highest level character can easily make in gold in 1 hour. As long as high-level characters buy low-level materials and items for their twinks, the price of these materials and items depend on the income of the high-level characters, not on those of the low-level characters.
As long as the low-level character never visits the auction house, he'll be stuck in the low-level economy, where you look silver, and your training costs, repair costs, and flying fees are also in silver. As soon as he hits the auction house, everything is priced in gold. We won't be able to buy anything useful with the silver he looted. But on the bright side, if he has something to sell, he'll sell it for gold, and can then use that gold to participate in the other economy.
The downside for the developers is that they lost control over the low-level economy. Nobody really cares any more how much silver a low-level mob drops, or how much it costs to train a low-level spell or ability, it's all just rounding errors in the price level of the high-level economy. I can't think of a good solution for that, can you?