But we (or at least I) don't point it out. I tend to wince slightly if the error made it hard to understand what the other person meant, but then I move on.
If I did write posts to people correcting their grammar I would be a jerk, but I see nothing wrong in being quietly peeved.
I have now decided to go for my MA/PhD in English/Creative Writing so I can teach the subject I love. And so, hopefully, I can curb the 'txt spk' curse that has emerged in our society. Don't get me wrong, when I'm TEXTING, I use it, but only because there's a character limit. There is no limit on discussion boards, etc... I do go back over my post before hitting the Submit button. I type faster than the hamsters in my brain can run on their wheels... *snerk*
I go so far as to add a little note in my online personals (yes, I do that): If you cannot speak/write/spell properly, don't bother emailing me. If you want to impress me, use your language.
Yes, I am a writer. Yes, I do own several grammar books, including the hefty Chicago Manual of Style. Is my grammar perfect? Heck no. But it's a lot better than what I tend to read on a daily basis. I'm one of those sick puppies who will pick out grammatical and spelling errors in published books... I'm strange, and proud of it!!