Oh dear, I'm sure we'll all become self-concious now when we're writing
In fairness, I think that a lot of the errors which creap into messages here come from writing in a hurry, rather than a lack of knowledge
One of my pet hates is the missuse of 'can' and 'may' - 'can' as in being able to do something, and 'may' as in having permission to do something... e.g. 'can I sit down?' - well, you're quite able to sit down; what you really mean is 'may I sit down' - i.e. do I have your permission to sit down...
But, as I say, it's only a pet hate, and most people don't give two hoots these days!
Marylebone is another pet hate - I have always called it (and will continue to pronounce it) 'marry-le-bn' rather than 'marlybone' or 'marrylebone' (gosh...it's difficult to try and write what you say!)