here is our /etc/logrotate.d/syslog-ng.conf file:
compress
notifempty
missingok

/var/log/auth.log
/var/log/daemon.log
/var/log/errors.log
/var/log/kern.log
/var/log/mail.log
/var/log/messages.log
/var/log/user.log {
   rotate 4
   weekly
}

/var/log/courier.log
/var/log/postfix.log
/var/log/ldap.log
/var/log/maildrop.log
/var/log/sympa/*.log
/var/log/apache/*.log {
   rotate 7
   daily
   sharedscripts
   postrotate
      /etc/init.d/syslog-ng reload >/dev/null
   endscript
}

To force the running of logrotate now:
# logrotate -v -f /etc/logrotate.d/syslog-ng