Split Infinitives: My friend assures me that "only prescriptivist grammarians will harp about split infinitives, and that's because they're basing their rules on Latin where it is not possible to split infinitives" and that it's okay to split infinitives because "we speak a Germanic language, not a Romantic one." Oxford Dictionaries would both agree and disagree: "Avoid split infinitives in formal writing, unless the alternative wording seems very clumsy or would alter the meaning of your sentence." The Chicago Manual of Style and AP Style Manual also recommend not splitting the infinitive unless it is for deliberate emphasis or to avoid awkward construction. Yes, this is what I spend my time debating with my friends.
Capitalization: Doing editing for business professionals is a constant battle in controlling capitalization. They want to personify everything from the name of their company to the business tools they use: "Our Company is here to serve You!" and "Good Synergy is all it take to accomplish your Goals!" While caps indicate a proper noun or the beginning of a sentence, quotation or thought, using them to give nouns emphasis is very Revolutionary (as in 1776, not an idea that has the potential to change the world). If texting has its way, we won't be using capitalization for anything in the next five years. Incidentally, Germanic languages are the pretty much the only languages to capitalize days of the week and months of the year and well as street names, demonyms and the nominative singular pronoun.
End Prepositions: Your sixth-grade teacher might have insisted they were evil, but avoiding them can make you sound pretentious. Yet if you find yourself using them more than once every thousand words, you're probably not using very effective writing. The problem with end prepositions is that they have no object, which means the modifying phrase is ambiguous, which leads to unclear writing, which results in miscommunication, which can cause hurt feelings and wars and big fat "F"s on final papers.
Transitional Conjunctions: If you have never begun a sentence with a conjunction, I praise you for being a good student and listening to your teacher. However, this is another one of those formal-writing no-nos that has become commonly accepted over the past few years. While used for emphasis and to show greater contrast in ideas, it is over used, and I am more guilty of this than most.