(In response to Rachelle Gardner's recent post, I posted a comment that turned out to be rather long, though relevant. Figured it would do better as a blog post than a comment.)
Remember the movie The Pursuit of Happyness? The guy breaks all the rules about job interviews, shows up "dressed like a garbage man" and still gets the job. None of us, I think, would ever risk a possible job opportunity by dressing like a garbage man and showing up on purpose. But sometimes you just can't help it. I know I don't want to risk a possible agent or publisher liking my book by presenting them with a garbage man query. (No offense to garbage men! You guys are awesome! It's just a stereotype. Please still take my garbage out on Friday!) But you know, I suspect there are writers out there who have circumstances that have kept them from polishing their queries, their first pages, or toning down their word counts. Is it still possible for them to get published even if they disobey all the rules? Yes. But do I want to be one of those people if I can help it? No.
I have never known anyone to get upset about a query letter or manuscript rejection because they thought the agent or publisher was being unfair...at least in person. I've read about several people who get upset online though, and I don't understand why.
Just keep your head about you, and it will serve you well.