Sometimes there are no definite rules in English. Different styles (MLA, APA, AP, etc.) use different sets of rules in many situations.
None. We all agree to disagree :)
-There is disagreement about using the word, "entitled." According to an AP handbook, "entitled means a right to do/have something; do not use it to mean 'titled'." However, in a Chicago manual you can find sentences like, "...publication of your contribution ENTITLED,..."
-Other variations occur when dealing with apostrophes. Some styles write, "Charlies's friend" while others use "Charlies' friend."
Again, we all agree to disagree. Different styles have different preferences, so as long as you follow the style you are writing for, you will be right.