I would have to concur with anonymous, for I have seen in many instances where my first urge is to admonish those with so-called "horrible" spoken grammar, but at second thought I realize that it does conform to some sort of grammar. Being prescriptive is mostly antiquated, however I do think there does seem to be the need for some agreed-upons in the English language, if only for a commonality in understanding. Language change is unavoidable. So, maybe there should be two disciplines: a grammar of the written language, and also one of the spoken? To be ruled and governed (in whatever way) separately, for they both meet different ends.