I see a lot of 'worse' instead of 'worst' lately.
I would never correct anybody on a forum, but I have to disagree with people who say these things don't matter any more, or that the only people who give a toss are pernickety old pedants.
Just the other day I heard of a friend of dd's (under 40) who is involved in recruitment for a major company. She actually bothered to phone one of the applicants, who had a Master's and was otherwise well qualified, and told him that unless he sorts his SPAG out he is going to find it very hard to get a job at the level he's hoping for.
When there are a lot of CVs all much the same, you have to weed them out somehow.
And it's not the first time I've heard similar - the weeders-out in both cases being under 40, not finicky old fartettes.
I know there may sometimes be dyslexia involved, but so often it's a case of basic errors that should have been sorted out in primary school - it's/its, your/you're, there/their/they're, who's/whose, etc., not to mention definately and similar.
To tell people these things don't matter any more is IMO doing them a great disservice.
I used to teach English to (mostly) Arabic speakers, one or two of whom were not even literate in their own language. It used to take me just one two- hour session to sort out its/it's - it's is ALWAYS short for 'it is' or 'it has' - (it's raining, it's been snowing, etc.) - so if it doesn't mean either of those then you don't need the apostrophe.
I just don't understand why it's apparently so hard to get this into UK kids' heads - unless of course their teachers aren't too clear about it, either.