So if I send my bitcoins from MtGox to my own wallet.dat (I live in europe) I would have to pay import tax?
Actually, no. And that is the beauty of it.
The actual balance is stored by the whole network, not on your physical computer. So by "sending" bitcoins, you don't really change their physical localization. It's just matter of complex mathematical computations.
By sending Bitcoins, you give somebody else the rights of ownership to the bitcoins, but they don't move themselves.
Unless the judge decides that the value is not attached to the code in the blockchain, but to the key that provides the right of ownership.