Personally, I subscribe to the view expressed by Stephen Fry on a number of occasions: Usage is the final arbiter. Language goes through fads, trends and fashions on a regular basis. The meaning of words changes - through usage. Slang is the most obvious example of this. The same applies, albeit less obviously, to grammar.
The rules of grammar, punctuation and even spelling exist for one reason alone. To clarify meaning. If the way an individual says something makes what they are saying easier to understand, then they have used the language correctly. It doesn't matter how many rules have been broken, only that the meaning of what was said is clearer.
The example of the 'split infinitive' is an excellent example of the grammar nazis getting it wrong. An earlier poster said that the 'split infinitive' was made up. It's actually worse than that. It was part of an attempt to impose the rules of Latin grammar upon the English language. It failed miserably. IMHO, the only reason anyone still thinks it's a 'rule' is because of the famous example from 'Star Trek'.