Bitcoin seems obviously like money to me. But I wonder when the IRS is going to start cracking down on other electronic money you can earn. Think about computer games where you can buy credits, or earn them by playing. That sounds like income tax evasion to me; you're getting paid in Green Rupees instead of US Dollars, but you should still be paying income tax on that! And don't forget about frequent flyer miles. (Which are not counted as income because you "can't" sell them, but anyone who reads flyertalk knows that's not the case.)
It's all very interesting. People have been using alternative currencies outside of the IRS's radar for quite a while, and they've mostly ignored them.