[ohgodthecat]

I believe that the salt is able to prevent rainbow tables because of storage capacity, as rainbow tables are quite large.

That makes the pre-generation of these rainbow tables quite impossible, especially with how long many salts are.

Now of course you can start generation when you have the salt but that doesn't really make any difference between just cracking the passwords as you go.

Whether or not it would have helped LinkedIN I can't really say but it probably would have been a bit better as people woulnd't have been able to compare the list to known passwords as quickly (but probably not much of a difference there if they knew the salt).

[sejje]

This is correct. Salt just defeats rainbow tables. They could still be pre-generated for high-value usernames, though.

Some say that this is most useful in giving the company a more sizeable window in which to react (e.g. force password changes).