It all depends on the context, though, gigilo.
On a forum like this it's easy to make allowances (no patronising intended) but where accuracy of communication is important then grammar and spelling are crucial.
My own view is that if I'm in a position to write correctly and accurately then I'm morally bound to do so, as a way of doing my bit to set a positive example.
If that pisses people off, it's something I have to live with. I can curse and swear with the best of them but tend only to do so for (usually comic) effect. Same with poor grammar and spelling.
On Sundays I read aloud in church. I often wonder if the people I chat to outside after the service wonder why I talk like Rab C Nesbitt in general conversation yet from the lectern I sound like a TV documentary narrator.
I have heard up speak on numerous occasions. You sound more like Kirsty Wark than Rab C Nesbitt.