What is the correct water to pasta ratio?

This question was answered to some extent in another Pasta cooking question by Roux. This answer, which is basically just a link to a series of experiments by an MIT grad / Chef, dispels a number of myths about cooking pasta. For instance:

• Water will return to a boil in the same amount of time regardless of how much is in the pot prior to pasta being added.
• Pasta won't get sticky with smaller amounts of water. It only gets sticky because of reactions in the first few minutes of cooking, and the solution is to stir it. This is necessary even with lots of water.
• You do not need a lot of water to cook pasta.
• Water does not need to be boiling to cook pasta. It simply needs to be above 180°F/82°C.

Some really interesting stuff in the article that debunks quite a lot of kitchen lore about cooking pasta. I have tried this at home with great success.

So in answer to your specific question:

• No, you do not need a lot of water, it simply has to cover the pasta.
• The amount of salt is heavily dependent on the amount of pasta, the amount of water, and your own taste. You need to find a consistent way to cook pasta and then experiment.

I prefer to use more water than is likely necessary, simply because when you add the pasta to the water, the temperature will drop some. The less water you have, the lower it will drop/the faster it will take to bring it back to a boil. Edit: This very likely may be a disproven myth, please read comment below.

Unfortunately I eyeball it based off how much pasta I have, so I can't give you an exact ratio. But I would err on the side of too much. Edit: I just eyeballed and then measured a pot, it looks like I use about 5 quarts of water for a lb of pasta. I still recommend erring on the side of too much, but now only because you don't want to lose too much to evaporation and end up running low on water halfway through cooking. Just enough to cover the pasta a little bit seems to work fine at our house.

I have found that enough so that upon evaporation, you don't run out is the correct amount. But then again, using too much takes longer to boil. I try to find an optimum based on these two factors.

My rule of thumb is 4 qt. of water per 1 lb. of pasta. This comes from a Cooks Illustrated article (I think from around '00) that suggested that this was the best way to keep pasta from sticking to itself.

That is nonsense. The more water per pasta ratio will result in less recovery time, which is more desirable. It's simple. Boil a gallon of water and add an ounce of pasta. The water will not stop boiling. Boil it again and ad a pound of pasta. The water will take time to recover. For dried pasta, every manufacturer recommends rapidly boiling water. Aldente reqires high heat to cook the outside of the pasta, leaving the inside slightly undercooked. This is were the "snap" comes from.