Mined bitcoins are taxed as earned income.
Depending on the specifics, that has the potential to be a massive problem. Let's say you mine $1,000,000 in bitcoins but at tax time, the BTC market crashes and they're now worth $100,000. Do your tax bill now exceed your income?
This isn't a hypothetical scenario - During the .com 1.0 boom, some people cashed in their stock options but kept the stock (to get long-term tax rates on stock that could only go up). A year later, they owed income tax (historical market price - strike price) on stock that was now worthless. (capital losses are limited to $3,000/year but carry forward).
That hardly seems fair. What possible reason could justify that?
It doesn't mean an offer to buy/sell at those exact rates (e.g., EUR/USD spot rates at every second will definitely be different from the 'official' accounting rates), but it's a guideline to evaluate value of things nominated in that currency.
What I find curious is the asymmetric handling of realized exchange rate profits vs. losses. Profits are taxed as capital gains, but unlike with e.g. shares, you can't use realized losses to offset the profits.
I don't know if they quality as "official", but probably good enough for taxation purposes.
