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 more info)

The taxation of barter (and the currencies that facilitate it) is a bit backwards from what we're used to - you are not taxed for receiving the barter "credits," like when you receive cash. On the contrary, you are taxed when you receive the value of those credits in bartered goods or services (like when you spend cash). In other words, you may receive DenverDollars in exchange for a product or service you provide, but you don't get taxed on the DenverDollars until you spend them.

The only real exception I know of is "Time Dollars," which have been deemed by the IRS as non-taxable, one reason being, "They are backed only by a moral obligation and are not legally binding." More information about this can be found on their site, http://www.timedollar.org

Is an off-shore, electronic currency taxable?