I have never taught elementary or middle school, but I do have the feeling that grammar and punctuation may be taught poorly or not at all, particularly by younger teachers, who often seem quite insecure about their own knowledge. This leaves it to those of us who teach at a high school or college level to deal with the problem. My own preference is to teach mini-grammar and punctuation lessons, using students' work as my jumping off point, because, while I do believe most care about communicating properly when necessary, it is very hard to engage students in lessons that are not about their own writing.
I am not particularly troubled by the writing I see on this site, choosing to put a positive spin on it. The students feel comfortable enough to communicate with us in their own way, which is good, I think, they are sometimes under time constraints, and it's better for them to ask improperly than not ask at all, and finally, we do have an opportunity to help them by editing their questions. Sometimes I wonder if I should take that extra minute to sneak in a grammar or punctuation lesson when I do edit a question, but I'm not sure whether or not I should be doing so.
As we do seem to be in the middle of a major shift, I cannot help but feel that as this generation learns how easily misunderstandings can arise without proper grammar and punctuation, these will fall back into place or be replaced in some other way. Can we look forward to a future in which emoticons are expected to clear up all misunderstandings?