You generally don't get taxed for holding personal goods, except real estate, at least in the US. I'm not a tax specialist, but it seems likely you would only get taxed on bitcoin transactions, ie: if you sell bitcoins for U.S. $ you would get taxed on the profit, much like a stock.
If you mean use bitcoins to avoid any taxation at all, well, I guess you better have a bunch of lawyers lined up.
