GNOME power saving settings has only a minimum part of its features available to be tweaked through the graphic applet in System -> Preferences -> Power Management. The vast majority of them are instead tweakable through gnome configuration editor:

gconf-editor

the main path is:

/apps/gnome-power-manager

There you can for example set the brightness resulting from the automatic backlight dim in

backlight/idle_brightness

and the time after which the screen brightness dims in

backlight/idle_dim_time

the idle time after which spindown the harddisk in

disks/spindown_timout

and whether require a password or not when GNOME resumes from suspend/standby or hibernate in

lock/gnome_keyring_hibernate
lock/gnome_keyring_suspend

this is particularly handy when you do not want to set a screensaver password but you want your computer to prompt for the password after you have suspended/hibernated it or vice versa do not want to have to type the password after setting th

Related posts:

1. Linux Power Saving Tweaks for HP Pavilion laptops
2. laptop-mode and hard disk monitoring software
3. Reclaim vertical space in Gnome!
4. Tweak GNOME gconf-editor from the command line