I ran across this video a while ago on what can happen to you if you don't pay your taxes. At some point during your Bitcoin career, the cryptocoin will be converted to fiat and that's how they will catch you.
https://www.youtube.com/watch?v=hf2fNEUPjQwWhen converting by itself, you have to pay, and so far there is no regulation for what to pay for the air. That's when there will be control over the crypto currency, then of course it will not be very sweet for us.