I'm sure most people have run across the person or three who doesn't understand the concept of chewing with their mouth closed. Bits of food are sloshing around in their mouths as they try and recant the story of their day, and then inevitably some flies out in your direction. "Ugh," you recoil, "close your mouth when you eat!"
Now as surely as I posit that table manners still very much matter, I would add to that statement...to a degree. At least in the US, most restaurant experiences are fairly casual when it comes to utilizing old 19th and early 20th century table etiquette. Not too many people are going to look at you with utter disdain if you happen to use your dinner fork to eat the salad course...and that's if you're even eating some place that actually offers courses, rather then here is your dinner all scrambled together on one plate.
We just don't really live in a time period in the 21st century where strict table manners matter so much anymore. People have come to the realization that, well, it's just food, and as long as you can basically manage to chew with your mouth closed, keep your elbows off the table, not dribble down your chin, or shoot the shrimp you're trying to eat right off the table, you have obtained some form of recognizable civility.
Now of course if you move up in society to the upper echelon where formal dinner parties, state dinners, and formal weddings become regular activities in your event calendar, it may behoove you to take an etiquette course so that you may avoid offending the head of state or someone's 90 year old grandmother who grew up being forced to abide by the rules, but for most people, knowing a basic thing or two about proper table etiquette will get you through most if all dinners you will ever have in your life.
I do however think it's important to remember that you shouldn't thumb your nose up at the idea of proper etiquette or table manners when you are a guest of someone else or dining in someone's house because you are a guest, and just like laws of another country, while you are there, you must respect the rules of the establishment or you may find yourself never being invited back.