In America, a pasta dish is often used as a secondi (ie an entree - the use of the term entree for a main course is American). Properly done, the pasta is a small dish primi followed by a meat (eg braciole) and vegetable secondi. Well, in America we do whatever the heck we want but at Maggie's HQ we try to respect the time-honored Italian traditions.
For me, any pasta as a main meal is a disgusting, bloating, cloying, enervating, fattening, brain-numbing experience. Best for a small dish primi, for special flavors. Same applies to risotto, gnocchi, or polenta. American restaurants serve too much primi to fill you up on the cheap.
Most common American error is to dump the sauce (or "gravy") on top of the pile of pasta. Nope. Dump the pasta in the hot pan of sauce and serve thinly-coated. That's what pasta tongs are for.
Others:
Don't Make These Sunday Sauce Common Mistakes—Or We'll Tell Nonna