Bitcoins are not "taxless." The IRS has issued virtual currency guidance. This updated article explains the basic principles of taxation for bitcoiners to be aware of when using bitcoins.
Bitcoin and Taxes
This book is well written and makes a complicated issue easy to understand. The subject of bitcoin is becoming very topical but there is little good material that answers some crucial questions like this. I read another informative article called "Some Basic Rules For Using 'Bitcoin' As Virtual Money' in the ABA Journal by this same author. Intellectually interesting material - makes me want to learn more.