Is easy to know when a non english speaker is writting?

Once upon a time I wanted to be a Linguistics professor.  I actually got an M.A. in the discipline before my life made a thoroughly enjoyable left turn.  At any rate, my masters thesis focused on English Grammar.  And lemme tell ya.  When it comes to grammar, English is a veritable rats' nest.

frigging gringos are trying to figure out my accent... hilarious !  

Yes. But I really enjoy what one of the above posters refers to as offbeat syntax. A few years ago, I was on a music forum and a French lady reacted to a particular new record by saying "I'm on the ninth cloud." Turns out she was saying the equivalent of "Cloud 9." I enjoyed that expression so much that I drop it on people every once in a while. The blank stares are hilarious.

Yes its easy to identify a non-native speaker unless of course they speak and write perfect English.  I know a woman from Belgium who speaks perfect English with no accent at all.  But she's the only European I've ever known who did not have any accent.  

 My wife has a niece who was born in Deutschland. Came to America at age 10. Speaks  perfect English no accent.  Asked my wife who was also was born there how is her German. She said perfect no German accent. Cannot tell the difference from adult Germans. My wife came to America at age 17 and has a mild  English accent. Thought is was interesting. I think at a  certain age one can do both perfectly.