(written as of patch 1.09, although the problem has been around for a while now.)
Diablo games have a currency, gold. It was too volatile, disappearing when you die, so people started using perfect skulls for trade. They were easy to find, but rare enough to mean something.

Then The Stone Of Jordan became the basic currency. At first, you could trade 5-8 perfect skulls for one. Eventually that went away. The SOJ is very rare, near impossible to gamble, and the basis for the economy... In real life, it'd be something like this:
Imagine the things you need to survive, and even some you don't. Now imagine that the $100 bill is the base currency, yet is still as hard to earn as it is in real life America. Imagine a world with little competition, so even people selling worthless bread or rocks demand $200. Imagine that no matter how many $10 or $20 bills you have, you can never trade them for a $100 bill. Lastly, imagine that counterfeiting runs rampant, and every so often the government destroys all insufficiently laundered counterfeit.
This situation happens because Stones of Jordan are by far the most duplicated item on battle.net, and new patches delete dupes. If the duplicate has switched 4-5 hands, you're OK... but sometimes after a new patch you'll find your 'currency' gone because it was illegal.
In conclusion, Blizzards intended barter system didn't work. Its very hard for a newbie to break into the economy, because although people are fond of charging outrageous prices for simple things, people won't pay much for stuff and will try to rip you off with fake-SOJ-cracks that turn into regular rings after the trade. I have my own supply, but nowhere near the 24-40 asked on USWest for only fairly decent items I want (trang-0ul's set, f'instance.)