There's a few keys to using salt.
First, you need to use freshwater aquarium salt. I don't know it to be fact, but I'm guessing that the ancillarly chemicals like iodine in table salt in the high amounts needed can cause an unsafe condition.
Second, you have to build up the salt levels. I've had a lot of luck with 25% of the total concentration every 12 hours. It takes 2 days to get up to strength, and it can probably be done quicker, but I've never done wrong with going slowly.
Finally, the end concentration that I've had luck with is 2TBSP per 10G.
I do believe that high temps will kill most strains of ich. I had one a few months ago that was resistant up to 90F, and man, fish are on fast forward at that temp.
I have ich in my hospital tank now, and I'm trying to treat with only salt. We'll see if it works.