Yes, very much. People who live near the ocean know this. The reason is that the process of rusting involves electrons moving around, and electrons move more easily in salt-water than they do in clean water. A simple test of this is to see how easily current flows in clean water (it does not), and then add salt to the water (then current does flow easily).

Yes, it accelerates it . Water is the enabler of fast oxidation of iron so freshwater will also cause rust. However, salt water is a very good conductor (lots of dissociated ions) and so there are a number of electrolysis reactions that tremendously accelerate corrosion in salt water. For example if you have iron in contact with salt water and also in contact with another metal such as aluminum (also in contact with the water) you effectively get a battery which drives very fast corrosion processes. This effect can be reversed by using a metal (like zinc) which causes the current to be reversed and in effect the zinc corrodes rapidly, protecting the iron. This is the principle of a 'Cal-rod' which is used to slow the rusting of hot water tanks (almost all of which are cast iron). There is a lot of information on corrosion on the web...