Kurt Eichenwald, for Vanity Fair:

But the reason for the price jump is almost irrelevant. What matters here is that the experience shows that the Bitcoin is not functioning like a useful currency. Think about it—would you cash in a share of stock at $13 if the price was zooming up? Or would you wait to see how high the value might go? Principles of smart investing dictate that you should sell when you’ve made reasonable profits, before an inevitable turnaround. Few ever follow those rules, including Bitcoin buyers.

I haven’t even joked about Bitcoin on Twitter because I didn’t feel like I understood it well enough to make fun of it. Eichenwald explains it well, and why it’s not a currency, it’s a risky investment.