The taxation is about the excahnge, not the currency. So an American citizen who gets paid in an off-shore currency (be it national or otherwise) is still responsible to report that pay and pay income taxes to the IRS.
Mickki is right about reput...
Reputation currencies that are not used for exchange shouldn't be taxable, because there isn't an exchange taking place. Exchangable currenices, even those considered 'alternative,' etc., are taxable under IRS barter tax laws. (See the IRS site for m...