Grammar is important, and it has not been taught in most American schools for many years for a very simple reasons: most teachers do not know enough grammar to be able to teach it. All prospective English teachers should have at least some linguistics as part of their curriculum; in fact, all English majors should, for without a strong background in the language it is difficult to really understand great literature. On the bright side, grammar is now being taken more seriously in the publishing world, and the evidence for this can be found in the proliferation of certificate programs in editing. Grammar is always a major component of these programs, and rightly so.
I keep hearing people say that "sticklers" spoil language; you have to "loosen" up. To them I would say that we have only language with which to communicate, and if we don't do our best to say what we mean and mean what we say, we are lost. Sloppy speech, whether written or spoken, starts a chain of miscommunication. Remember, at our best, nothing is totally communicated from one person to another. Never. Considering this, how can we do less than our best if we are ever to honestly say anything to each other?
In response to the comments of others, I would like to add that although fiction doesn't always follow the rules of standard English usage, it is important that the writer of fiction understand the rules before deviating from them. Picasso learned to draw before he went abstract; he didn't make all those funny little marks because he couldn't draw, but precisely because he could! That is what gives control.
The truth is that you have to learn the rules before you can break them.