Punctuation and grammar are important. The way we write tells a lot about us. Even if we don't think it is important to follow some of the rules, it will at best show that you are not concerned about following something that is an established standard. At worst you can be easily interpreted as someone who is if not uneducated than at the very least lacking in many respects. On one end, it is very superficial and can lead to some presumptuous judgements or making a poor first impression. On the other hand, it is the writer's fault for assuming that others have just as loose opinion on certain standards and disregard 'arbitrary' (but then again you are guilty for saying that something is arbitrary… arbitrarily ;P) rules.

One thing that this discussion has shown me is how very different the rules of grammar can be in different geographic locations. The discussion made more sense when it was revealed that the OP is from Canada, given some of the rules that were discussed.

As a person from the US, the "correct" spelling of neighbor doesn't have a u in it. Period. :p

In a somewhat related way, I can usually tell within a few sentences if a person is a non-native to the US speaker. While I agree that poor grammar can be a problem that annoys me, I also try to realize that people on the internet are writing from all over the world.

Should that affect the local rules for grammatical correctness in formal writing? I'm less sure of the answer to this as time goes along. I'm influenced by intelligent non-native English speakers and native English speakers who communicate well despite their relatively poor grammar.