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.
Tax should be payed because that's an obligation as a citizen. Yes it will be difficult for the government to track down your profits but sudden increase of purchases would be questionable. Just to be safe, pay taxes it will be much cheaper hiring a lawyer than paying tax.