"Let's eat, Grandma!" or "Let's eat Grandma!"-- Do punctuation and grammar really matter?

 Warning:  I am an old school grammarian.  I love diagramming sentences, prefer essays be written in 3rd person, and almost had to re-take my English comps because I had a sentence fragment (a dependent clause standing by itself over two-thirds of the way through the examination).  (I, also, do not like slanted fraction lines, but that is another story for another day.)

Two things recently caught my eye that spurred me to write this discourse.  One is a Facebook webpage,  Lets-eat-Grandma-or-Lets-eat-Grandma-Punctuation-saves-lives/276265851258?v=wall&ref=mf, a friend sent me the other day that inspired the title.  The other source was my recent readings.

As I read more and more contemporary writing (fiction, non-fiction, blogs or internet articles), I am beginning to wonder if grammar and punctuation truly matter anymore.  Sometimes I am not sure if the things I am reading have been edited and if they have, I wonder about the background of the editor.  The rules of formal writing seem to be disappearing, though I think part of the issue is the desire to get the books to the market as quickly as possible.

(As I am writing this, I have been checking my Facebook page and I just noticed that one of my friends became a fan of this page--  "Blasting music when your pissed".  I wonder what is pissed.)

In this e-mail/twitter world, the emphasis does not seem to be on form as much as it is on function, but is there any function in what is written?

I teach at the collegiate level and I find that my requirements for grammar and punctuation amaze many of my students.  They tell me that few of their other instructors require them to be so precise.  Is that because they do not (I even have a hard time using contractions) know any different, or they don't care?  I'm not sure which is the case.

But the publishing world and the academic world are not the only places where this decline seems to be occurring.  I also see it in the business world as well!

So, my question is this, does it matter anymore?  Just as we have become more relaxed in our mode of dress, should we accept the relaxed attitude toward grammar and punctuation and just assume that we know what is attempting to be communicated?  Do I need to change the way I teach?

(For those of you who still appreciate the fine points of grammar, check this link Grammar Girl, though she makes some concessions.)