But if you're paid in bitcoins, you still need to report that income.
A taxpayer who receives virtual currency as payment for goods or services must, in computing gross income, include the fair market value of the virtual currency, measured in U.S. dollars, as of the date that the virtual currency was received.
The same rules apply if an individual mines bitcoins -- "the fair market value of the virtual currency as of the date of receipt is includible in gross income."
In other words, if your salary gets paid out in bitcoins, that money would be taxed just like a paycheck. But if the value of those bitcoins goes up after you get paid, that extra gain would be taxed just like any other investment, at the regular capital gains rate.