It seems that in 12.1, root can no longer 'su' into an account with no password. Stupid me didn't check rc.mysql to see if the directions changed. They did. It now says to use:

mysql_install_db --user=mysql

However, now I need to know if I need to recreate the mysql user because I deleted the password for it. (before toggling the password with 'passwd -u/-l mysql would always show that the account is locked when typing 'passwd -S mysql' but now it toggles between L and NP (locked and no password)

Also is this new functionality of 'su' something to do with slackware settings or a newer version of 'su'??

Well I did not mess with mysql user on my system (slackware 12.1) and the output with passwd -S mysql shows:
mysql L 10/28/1996 0 -1 -1 -1
So it seems locked by default
BTW I use mysql here, works fine

my mysql is retarded and dies upon boot =(

I don't know why Patrick J. Volkerding takes the effort to write how to properly configure mysql in Slackware (script comments in /etc/rc.d/rc.mysqld), nobody seems to read it :/