Like many things web related, expect many proclamations of the "success of Bitcoin" and "the death of Bitcoin" long before a sustainable trend is established. The Bitcoin economy I believe is currently estimated at several tens of millions of dollars annually, but growing at a fast rate. Also remember that the vast majority of fiat currencies have failed (and those that have not are devaluing quickly), mostly because of devaluation and often because the issuer of that currency has crumbled (often from loss of military power). So the appeal of a hypothetical non-fiat (by fiat, I mean government fiat), decentralized, private currency are great across the world.
Money systems are about control & taxes. Bitcoin is supposedly about more freedom. The US dollar system for example is controlled by a cartel of banks and affiliated companies that take a cut of the economy with every transaction.
I believe I heard that Amazon for instance, pays about a billion dollars a year in transaction fees for example. If I was in charge of Amazon, I am sure it would be interesting to accept payments in a system that negates the need for all kinds of middlemen in the simple act of accepting payments. Of course if you are a government collecting taxes, you are going to pressure large corporations to not use Bitcoin. You will do everything in your power to vilify alternative currencies, it is the only thing they can do to prevent most people from using it. The government could make Bitcoin illegal for use, but that would simply cause an appreciation in value of Bitcoin. Without a way to enforce use of Bitcoin, it may be a losing gamble for said government, especially since their main business and control is their competing fiat currency.
In the long run, over the next few decades, I think a private, decentralized open source currency is bound to become pervasive, especially as the Euro and other fiat currencies decline in value, as have the vast majority of fiat currencies before them. Whether Bitcoin is THE currency to replace, remains to be seen. It may be one of a host of similar currencies with similar concepts used in different ways for different uses (store of wealth, vs. value transfer vs. investing, etc.)
Here is a rather comprehensive introduction from a libertarian source: