Oh my god, ALL OF THOSE are huge pet peeves of mine. I don't have perfect grammar, but I feel like I have better grammar than most people.
Fortunately, the 3 forums I visit most frequently all have memberships with at least decent grammar... there's a regional board I go on occasionally, that you would swear was comprised entirely of elementary school students. It's awful. What's worse is some of these people are police officers, business owners, etc. I have a very hard time taking these people seriously when they make simple spelling mistakes, or don't even TRY to type properly.