There's been a flurry of Bitcoin critiques all of a sudden. This is the most comprehensive I've seen (so far).

In short, there is the possibility of an unforseen technical - in the IT sense - problem with the overall security of the Bitcoin system, and there is the technical - in the economics sense - problem of how a currency which is designed to be deflationary, with no available corrective mechanisms, would work. If you know the value of Bitcoin can only go up, there's a stong incentive to hoard. But if everybody's hoarding and nobody's actually trading in Bitcoin, where's the real value? Pop!

The inescapable reality of any kind of monetary regulation is that decisions of when, where, and how to allocate resources are inherently political. As Adam Smith would tell you, there is no economics but political economics. There is no hands-off, one-size fits all regulatory system — whether it be trust in an algorithm, a relatively rare chemical element, the infallibility of unfettered markets, or the inevitable tendency of history towards communist utopia — that works in anything but the short term for a fraction of the population. In the end they all crash, and conscious decisions have to be made, hopefully democratically. In fact it would be a jolly good idea to build democratic decision making into the system, but that was the project we all decided to abandon about 35 years ago, and hasn't that gone swimmingly? In the short term. For a very small fraction (some would say 1%) of the population.