What are some things to consider when choosing a salt?
Most of the issues come down to the additives and the shape of the salt.

Some people find that iodized salt gives some off flavors, while sea salts will have regional differences in their mineral content that affects the flavor.

In my mind, the bigger issue is the shape of the salt:


Kosher / flake salt : See Darin's comments for examples of some of the benefits.
Pretzel salt : large crystals, gives a crunch when eating it.
Popcorn &amp; Pickling salt : fine crystals; will disolve in room-temp water and stick well to relatively dry items.  Pickling salt is uniodized.
Rock salt : good for salting paths and salting ice to bring down the temp when churning ice cream.


For general baking, or salting water for cooking, I tend to stick with cheap, old fashioned table salt, in part so I don't have to convert recipes.  And I use iodized, because I don't eat out much, or eat much seafood or processed foods.

For general cooking, I tend to use kosher salt, mostly because I keep it in a container I can easily get a pinch of.

I've never bothered with most gourmet sea salts ... maybe I'm not using enough, but other than smoked salts, I don't really taste the difference.