Recently, out of the blue, my installation of mysql suddenly stopped working. The daemon was dying with the error of
040512 04:32:11 mysqld started
040512 4:32:12 Can't start server : Bind on unix socket: Permission denied
040512 4:32:12 Do you already have another mysqld server running on socket: /tmp/mysql.sock ?
040512 4:32:12 Aborting
After backing up my data directory for mysql, and reinstalling mysql several times, the error persisted. Upon further investigation, the /tmp directory (where mysql keeps its lock file) had somehow become a standard directory, rather than a symbolic link to /private/tmp/
Deleting the offending tmp directory, and reestablishing the symbolic link, finally fixed the problem.
Anyway, just wanted to pass this on, in case this ever happens to you.
[ps... and no, mysqld wasn't already running, and there was no mysql.sock file in the hosed tmp directory, that's the first thing that I looked for]