Grammar is used to structure a text and make clear what the author means. Without grammar it gets really hard to make clear what you mean. For me, as a non-native speaker, proper grammar and spelling is even more important. This is because I don't have the instant associations which native speakers do have, even though I am quite proficient in English (even if I say so myself). That being said, commenting on someone's grammar or spelling over the internet is usually wasted effort, even with the best of intentions. It is often seen as a personal attack and takes all intelligent discussion out of the thread. As a result, I never comment on grammar or spelling. I do, however, think that most spelling errors can be prevented since we have all those spell checking programs build right into the browser. I do agree with you, you are not turning in a paper for a grade, but you are trying to communicate an idea. Grammar can greatly improve the clarity of any piece of writing and help you make clear what you mean. Anyway, just my 2 cents ;-)
As another non-native english speaker, I make snail's words my own. On the internet, where conversations take as much, if not more, from speech than from formal writing, "proper" grammar and spelling should be the least of our worries.For me, as a non-native speaker, proper grammar and spelling is even more important. This is because I don't have the instant associations which native speakers do have.