The problem is that for many people, it does't matter as much. If you have bad grammar, or write poorly, it won't matter because so many other people have bad grammar and write poorly as well. You don't see anything wrong with it.
It's usually simple things to: capitalization, punctuation, proper tense, and spelling. I understand typos occur, and sometimes people just don't know better. Fine. The biggest problems are the use of chat words, like "u" for "you" and other problems. People use these in a casual atmosphere, and I feel it becomes normal for them. They see proper writing as work.
Meh, I dunno, mybe i be tinkin 2 much abot tis.