I don't find "Yanks" insulting, for what it's worth; kind of charming, in my opinion, even when used by people from south of the Mason-Dixon line. And "Americans" excludes a lot of territory to the north and south, and "People from the United States" is a mouthful.
My wife, on the other hand, spent her high school years in Canada during the Vietnam war, and she tells me she often heard it in a derogatory context, so it troubles her. And of course back in the mid-20th Century, we heard a lot about "Yanqui go home" from our southern neighbors ... so maybe I'm under-sensitive :)