Seth Godin says that when he reads something with the misuse of its and it's or unnecessary quoting, he assumes the writer is stupid.
I've had people suggest that this no longer matters, that it's all about the message and that people will know what you mean.
Does it still matter?
Yes.
(I agree with Seth. While the assumption of stupidity is our own personal failings, it still happens and we're probably not alone in this.)