It's ridiculous- my English teacher thought ignominious meant 'special' and spelt falsify with a 'c'. A fucking 'c'. Those are only two of his countless errors which border on ridiculous. And yet he is (supposedly) teaching me English.
I agree with those who say that as long as you can get your message across, you have sufficient knowledge of English, but there are limits.
When communicating on bos for instance, or msn, abbreviations, contractions and whatever else takes your fancy is fine as long as it makes sense.
But when necessary people should be able spell words correctly and construct grammatically sound sentences with such ease that thought isn't required.
That's called being fluent in a language and anyone born in any country should, by definition, be fluent in their mothertongue.