I don't mind sentences that end in prepositions, as long as rewriting the sentence to avoid it would have made it more awkward. Passive voice, when used properly, rules. And, sentences that start with conjunctions are okay too. But, dammit, it's "I'm doing well," not "I'm doing good." You can do good, but that means you're doing good works, not indicating that life is peachy.
I usually consider spelling, grammar, and punctuation to be fairly important, though I prefer an informal writing style, which allows some of the harder rules to be ignored. Usually I accept these grammatical rules without question, either because they make obvious sense, or because someone else thought of them and they seem "good enough." You should always have a comma before "and" if there are at least three items in a sequence. It looks better, it looks like it sounds, and it's consistent. But, there are a couple rules that I really just don't like.
I think it's time to reevaluate how we set apart titles of artistic works. I'm talking about movies, books, paintings, songs, albums; the whole works. We quote songs. We italicize (or underline, for the truly old-school) book and album titles. There's dispute over paintings and movies and poetry. I don't see a good reason for any of it. They're proper nouns, and thus we already capitalize them. Isn't that enough? I feel the same way about ships. Why do we italicize U.S.S. Constitution but not Paris? Not even God gets italics. Who's to say that we should italicize Larger than Life by the Backstreet Boys, but not Martin Luther King, Jr.? I say we get rid of quotes (or "quotation marks," for the people who care even more about this than me), italics, and underlining from these sorts of things. Our current system is just stupid, it's confusing, and it doesn't seem to serve a very useful purpose.