I do not use salt or mineral licks and have been advised by my vet to avoid them.
A good pellet will provide the salt, vitamins and minerals needed. Salt and mineral licks can be dangerous as a rabbit can go months without using it, then eat the whole thing in a week. This will lead to imbalances and other problems. Think about what happens when people eat a lot of salt, they can get heart problems and high blood pressure. Mineral stones have a lot of calcium which can be a problem for many rabbits and can cause bladder or kidney stones.
I didn't know that they shouldn't have a salt lick either and had one in Rocky's cage when I first got him. He didn't really like it though so I didn't get another one. Then I read in here that they shouldn't have it. It is upsetting that they sell them for bunnies in every pet shop it is hard to know what to give and what not to give :S
I second that; I am frustrated with pet stores marketing products because the big giant heads in the corporation tell them to. There's so much crap out there...I can't tell you how often I go shopping for rabbit AND ferret stuff and compare ingredients based on what the diet SHOULD consist of and falling way short.