We have had more than a few clients this past year ask about Bitcoin and trading in Bitcoins from an income tax perspective. There has been a lot of urban legends out there that claim, since the IRS has not given any formal guidance, that income taxes don't apply. Like most urban legends, that is simply wrong and making that assumption can land you in some real tax trouble.
When we delivered that news it was sometimes not what our client, or prospective client, wanted to hear. We've had to remind everyone that the primary premise of the U.S. Tax Code, Section 61, is pretty simple. It says that "gross income means all income from whatever source derived." So, unless there is a specific exclusion from taxability for the income source, you're on the hook for taxes.