I don't do it (well, not on purpose) and I really notice it when others do it as I can 'mark' word processing so it stands out a mile. I wouldn't comment on it though as this is not school or some sort of test.
I've never noticed it anywhere before, but I think I would find it annoying if people started doing it everywhere. I don't think it makes it easier to read.
I did say not just on here Sher. Yes, a current post brought it to mind to ask but I've actually noticed it tons on twitter and like I said, people at work. And apart from asking him why, I've never mentioned it to any of the others.
Oh yes Snags. Multiple !!! is another major annoyance. I have a sister who can't write a single sentence without !!! At the end of it. It bothers me so much I told her I won't reply to her texts unless she stops doing it. Although I don't like her much anyway so it suits me.