Thanks to you and astine, I just learned today about per-user salts. I thought that you only needed a site-wide salt and after reading on the topic, I now understand why it's better to have a per-user salt stored in the db.

I was also confused by these frameworks (e.g., Django) that ask you for a secret key and I thought that the secret key was a site-wide salt. Fortunately, they knew better than me ;-)