Are we really good with this? Well, no.
Is 'I'm good' really a universal American response to 'How are you?'
There are two important milestones of assimilation for a Briton living in the United States, according to Johnson, The Economist's language blog. One is to start calling the final letter of the alphabet "zee" instead of "zed." The other is to start responding to "How are you?" not with "I'm well," but with "I'm good."
I'm not so sure. As an American in Toronto a few years ago, I found the zee/zed transition in the other direction surprisingly hard, but I felt I had to make it because so many people seemed simply not to understand "zee." Surely "zed" would be even more baffling to Americans. So I think zee-for-zed would be a conscious decision early on rather than a sign of having finally gone native.
And I'd agree that any Brit who said "I'm good" instead of "I'm well" probably was pretty far down the path to Americanization. But is "I'm good" really a universal Americanism? Please, someone, tell me it's not. After all, you don't really have to say, "I'm well," if that sounds just too upmarket for you. There's always "Fine, thanks," for heaven's sake. Oh, and will you please hand me the sugar tongs when you're through with them
The blogger Grammar Girl is often on the side of the (prescriptivist) angels in her advice, leading her readers through the wilds of lie versus lay, for example, and illustrating her points with quotes from lyrics of songs by Bob Dylan and Eric Clapton. But she came out a few years ago with a stout defense of "I'm good" as a response to "How are you?"