[nhaehnle]

If one day Bitcoin gets truly popular governments will be in trouble. How to tax that beast? I wonder if there is any other solution then poll tax.

You would tax Bitcoins in the same way you tax transactions in USD, EUR, and so on. There really is no difference, once you stop to think about it.

Even with the USD, taxation does not work by the government subpoenaing your bank's records. Instead, it is your (or your employer's) responsibility to report your income and related data according to the legal requirements. The same applies to Bitcoin transactions.

Obviously there are some differences in the investigation of tax evasion. But there will still be records somewhere, and prosecution is used to deal with similar problems when transactions are cash-only.