[yason]

Where Bitcoin might run into trouble is the trading of bitcoins for dollars or commodities.

But even if trading was made clearly illegal in the U.S. all that we need is a company abroad under benign legislation that allows you to buy/sell bitcoins and that accepts credit cards.

You're right that you obviously can't make it illegal to perform mathematical calculations over big numbers. Also, you can't make it illegal to interpret the result of the calculations or giving them a context.

But I think you can't make it illegal to trade bitcoins either: if everything else fails we can always have bitcoin trading parties where the participants can exchange bitcoins to money and money to bitcoins with no third party in the middle.