I'm sorry, Martin. I used to believe that, too, but it's wrong. "I'm good" is perfectly acceptable.
Well people argue that "fast" is not an adverb, but an adjective, so you should use "quickly" instead.
"We arrived there fast" vs "We arrived there quickly".
I guess prolonged usage of something that has always been considered wrong, technically renders it correct after a certain while. Since it's being used by many, who's to say it's wrong?
In all honesty, I did say bad English, not wrong. There is a subtle difference. But I understand what you're saying.
If we're learning English, I would definitely say you have to do good/well the correct way. But as we're learning Hungarian, I would like to do grammatical errors that doesn't affect the meaning. We've still shown that we've understood the Hungarian sentence, that should be enough. – The same should go with mixing up is/are.