I've mentioned the Bitcoin project before, referencing it as being a possible solution to a lot of the problems surrounding money. Basically it's a peer-to-peer currency that's untracable and ultimately anonymous. Right off the bat you're pretty much going to be able to order drugs from sites like the Silk Road Market. Honestly, I'm not sure if that's the best use for the time being considering your package of Purple Kush may have to go through customs if you're not in the Silk Road's country.
But that's just one small aspect of this.
Bitcoins can be transfered as payment from online companies or just the Chinese gold farmer who got you that epic set on WoW. There are already companies out there that are accepting Bitcoins as payment (check it) and I'm sure as the currency grows, more and more companies will switch to the currency.
At least, that's before world governments start getting pissed about the fact there's a global currency which they can't tax. They'll also be pissed about the fact that there's no central issuing authority they can prosecute or buy out for Bitcoins. It's all based on algorithims which produce the Bitcoins on a rate of how many users are on the network which is all explained better on the BitcoinFAQ.
Really, Bitcoins work under the same supply and demand principle and basic stuff you'd find in any Economics 101 class, but this is the first time in the course of human history where we have a true global currency. Whether it will become accepted is highly doubtful. It'll probably end up becoming the currency on various darknets and the seedy underbellies of teh intarwebz (I'm looking at you 4chan).
I don't mind though. It's cyberpunk as fuck.