system logs are recorded in /var/log/ directory

boot log is at /var/log/boot
however to enable it you should make sure that file /etc/default/bootlogd has this string BOOTLOGD_ENABLE=Yes

other useful logs are
/var/log/syslog
/var/log/dmesg

and config files at
/etc/syslog.conf

a and /etc/logrotate.conf

gnome-system-log is a graphical applet to manage logs
to configure monitored logs enter gconf-editor and go /apps/gnome-system-log/logfiles and edit the key