I have been trading Forex CFDs on Oanda for some time now (before I was trading Forex on IB, but since they moved from UK to IE they do not allow leverage on Forex any more, so...) I have not seen any major issue, but I day trade so I don't care that much about a few dollar extra lost in the extra spread. Of course if I were to do scalping with OANDA that would not be viable as the wider spread would eat up my profits. As for shorting USD based on fundamentals it is always a risky business as you my correctly predict a fall for the USD but may be significantly wrong with the timing of it (even by few years). This is true for any instrument IMHO, see the movie "The big short" to see why...