I have mixed feelings on the whole grammar thing. On the one hand, language changes. It changes more slowly when it's written, because we set the rules in stone. And there's no denying that everyone adhering to the same rules makes it much easier for us all to understand each other.
Yet somehow folks with poor grammar generally make themselves understood, and grammar is really just a set of arbitrary rules in the first place. English's rules are especially messed up since many are a result of an attempt (by a couple of guys with too much time on their hands) to make English, a Germanic language, act more like Latin.
The upshot is, I used to care more about strict and proper grammar than I do now, because it is arbitrarily laid out. But the rules are still good to have.