I've been testing for about an year a Regulated ECN Broker that accepts US Citizens as his clients.
I know there are not many european brokers accepting US citizens and I've heard a lot of people looking for a Forex broker that accepts US citizens.
I have been testing their execution for manual trading and also for automated trading and also doubled my account. Live Stats here and you can see me trading Non-Farm Payrolls / NFP in this post:
In fact I started the tests in December 2012. So in about 8 months the account is double in size.
I hope it helps.
