I disagree. Salts are not secret. The passwords are. The idea is that it just prevents massive pre-computation attacks, where the same set of precomputed hashes

I disagree. Salts are not secret. The passwords are. The idea is that it just prevents massive pre-computation attacks, where the same set of precomputed hashes can be reused. At the point there are salts introduced (different for each user), there's no way to precompute a huge rainbow table and use it. So from my un-trained-in-cryptography eyes, the username approach is solid.