I have found that when adding salt just before adding pasta, that more is better.
But how much is too much?
What is a good ratio of salt to water when cooking pasta?
More is not necessarily better, but no salt leads to a bland final dish. Some folks are fond of saying "as salty as the sea." This sounds romantic, but probably has no basis. Pasta water, and the resulting pasta, can certainly be over salted. The internet shows results that are all over the place. Any where from 3/4 teaspoon to 2 tablespoons per liter of water. However, this also depends on the saltiness of the condiments you are using with your pasta. Unfortunately, there is no magic number.
I think the best you are going to find is "salt to taste".
I just throw in some amount of salt that looks about right, then stir briefly, taste the water and add more salt if needed. If the water tastes as salty as I would like a soup to be, the saltiness of the pasta will also be perfect for my taste.
To give a rough numeric value as well, soups generally contain slightly below 1% of salt by weight. For comparison, sea water has about 3.5%, which would be WAY too salty for my taste.
I'm pretty sure that Marcella Hazan recommends 2 tblsps. of salt per 4 gallons of water, I think in Marcella Says (sorry it's in a box :/). At some point years ago (through a process I don't exactly recall now) I determined that this meant I should use 14.2 g of salt per 2 L. of water for 1/2 lb. of pasta, which is more like what I usually make. I've done this for some indeterminate amount of years and it always gives excellent results. Other tips I learned from her are to stir the pasta for 30 s. after adding it to the water to prevent it from sticking, and to toss it immediately after draining in either butter or olive oil (depending on the sauce) at a ratio of 1 tblsp. / lb. of pasta. Priceless information if you ask me.