to ditch: you're the one trying to be offensive, so don(t blame me if you get some response back, no wonder Belgians say about dutch people they are all mouth and no substance; FYI: a local has no clients and just trades for his own account. I personally know several big derivatives traders in Amsterdam: they all pay taxes, on or off the floor. as danielc1 points out this is not a black and white situation, 10 years ago I went to managment of Belfox (Belgian futures and option exch.) to talk about this subject I they didn't even know how things were exactly for private investors. With what I know things are like he explains them now in Belgium. thanks for the link danielc1.
US citizens. You still have to pay income tax no matter where you reside. There is a break of 0 tax on the first $80-125K earned while living in another country. Not sure on cap gains, but I would think that is not going to be reduced for your US tax return. The only way out of this permanently is to renounce your US citizenship and become a citizen of another country, like Monaco for instance.