Excellent, this is always a little personal gripe of mine (and inevitably others I presume).
Americans speak American. It is loosely based on the English language, but over the years it has mutated (as it's natural for all languages to do over time) into what it is today.
But, by that process, it's not English anymore.
I was working with an American a few years ago, he was a great chap and we had a lot in common and got on fine, but I reminded him of the above and he couldn't understand my point. So I gave him an example. "do you realize" I said, "that you have just said to me... the Contractor received the instruction off of the Engineer". He blushed a bit and thought for a while, then said "what's wrong with that?"
Now I'm no genius, and I suffered in school from not paying attention to (or not being taught) English grammar lessons, either way I don't know the technicalities of language, adverbs, past pronouns and the like, but I do know, from extensive use, what is right and wrong, and "off of" in that order and in that context, is plain wrong. It doesn't actually mean anything in its own right.
I said "why not...the Contractor received the instruction from the Engineer", it's simpler and more importantly it's correct".
He just laughed and still to this day I don't think he understood my point. My job (and his) is predominantly writing technical, contractual and legal reports, so it's quite important to get the writing as "proper" as we're able in a formal document.
I've drifted from the point of Chas' post, sadly. But the facts remain and my gripe continues. Americans are free to speak whatever language they wish, but please, don't let them pretend it's English.