That will be stamped out on its own. If no one can understand a post, eventually the poster will catch on and adapt. Besides, I think almost everyone can understand a post, it just irritates their sense of gramatical propriety or whatever.
So the issue is if people have a duty not to irritate people with their posting style. I say they don't.
Wooo, a proper grammar thread. Or was I supposed to misspell grammar and then have someone catch me on it, and then I say it was a joke? It actually takes me longer to write "u" instead of "you" and "ur" instead of "your" because I'm just used to it. I think typing speed might have something to do with it.
On AIM, I don't capitalize the first word of each message, nor do I use periods. That's because each message is a sentence. However, I do capitalize my proper nouns and the like, and I use exclamation points and question marks. I'm glad I don't play games online where people use all kinds of shorthand and number substitution. I think I'd go crazy, or at least get a headahce.