Earlier quoted context omitted.
Remember salts don't need to be secret to do their job. The goal is to change the algorithm slightly (by adding additional input) for each user. That means you can't mass-precompute (rainbow tables), and just look up what matches, you have to break each user individually. Your reasoning about how salts work is correct. There's also something called a pepper which is another additional bit of input data, that is only…
Please refer to my comment above. You can precompute a rainbow table if you know the username (trivial) and the method of hashing[1]. Whilst usernames as salts would increase security over no salt, it results in a potential exploit / vulnerability that would not exist if the salt was truly random. Hence, suggesting the use of usernames as salts is not wise. [1]: http://en.wikipedia.org/wiki/Kerckhoffs%27s_principle
Re: 6.5 Million LinkedIn Password Hashes Leaked
#331I read cschneid's comment twice, and nowhere to I see where he or she specifically recommends using the username as a password; he or she simply recapitulates the logic behind using a unique salt value for each stored hash, and describes using an additional non-unique value which is not stored with the passwords ("pepper"), which is a new and interesting idea, at least to me.