Nothing grinds my gears more than when a writer does not know the difference between "you're", "your", "their", "they're" and "there"! Grammar and punctuation are not the meat of your story, but they are the framework that makes a good story stand out. Words have to be arranged to convey what you want to say, what you want a reader, such as myself, to take in. You cannot just put words in front of readers and expect them to arrange them into meaningful bits of information! Poor grammar and punctuation is the kill-all of any potentially good story. Fact.