In rh6.x if you su'ed to a "special" account, like postgres, you got the usual PS1 prompt. In 6.9.x the PS1 is exported in /etc/bashrc (instead of /etc/profile), which is sourced in .bashrc, which is sourced in .bash_profile; so that if you "su" to postgres you get "bash-2.04$" as prompt, since there is no /var/lib/pgsql/{.bash_profile,.bashrc}. Don't know if this change in behavior is intentional (ie: to let the user know it's using a not-normal-account) but it doesn't look a nice thing to see :)
This is intentional - we've had to move PS1 to /etc/bashrc to fix other bugs (the bash-specific stuff in /etc/profile was preventing people from using other shells as /bin/sh).