Are you going to pay taxes on your Bitcoin profits?
Suppose you make a million dollars. Suppose you have already made a million dollars. Are you going to hand half of that cash over to the government? Of course, this is assuming you convert your coins into federally recognized cash. If your only intention is to amass a huge supply of Bitcoins, the question does not apply to you.
You're supposed to pay income taxes. It seems rather easy to get away with not doing it, though... at least in this case.
The dollars I used to buy bitcoin were already taxed, income tax withholding taken out of my paycheck. I owe no tax unless I "sell" at a profit and I'm not going to trade them back for dollars, so there are no capital gains. I will trade them at a later date which is considered barter and barter is legal.
Except for short-term cash-flow reasons, I can't imagine why anyone would trade a non-dilutable currency for depreciating bank notes. I'm never going back. Ever. Bitcoin is the real money.