Afin d’avoir un pc qui se met en veille et hiberne rapidement (» rapidement»  pour l’hibernation est un gros mot je trouve, encore bien trop lent à mon goût) j’ai réglé mon fichier /etc/default/acpi-support comme ci-dessous, je ne garanti rien, mais pour info le mien est régler comme cela et ça fonctionne très bien.

sudo cp /etc/default/acpi-support /etc/default/acpi-support.bak && sudo gedit /etc/default/acpi-support

# Comment the next line to disable ACPI suspend to RAM
ACPI_SLEEP=true

# Comment the next line to disable suspend to disk
ACPI_HIBERNATE=true

# Change the following to "standby" to use ACPI S1 sleep, rather than S3.
# This will save less power, but may work on more machines
ACPI_SLEEP_MODE=mem

# Add modules to this list to have them removed before suspend and reloaded
# on resume. An example would be MODULES="em8300 yenta_socket"
#
# Note that network cards and USB controllers will automatically be unloaded
# unless they're listed in MODULES_WHITELIST
MODULES="uvcvideo"

# Add modules to this list to leave them in the kernel over suspend/resume
MODULES_WHITELIST=""

# Should we save and restore state using the VESA BIOS Extensions?
#SAVE_VBE_STATE=true
SAVE_VBE_STATE=false

# The file that we use to save the vbestate
VBESTATE=/var/lib/acpi-support/vbestate

# Should we attempt to warm-boot the video hardware on resume?
POST_VIDEO=false

# Save and restore video state?
# SAVE_VIDEO_PCI_STATE=true

# Should we switch the screen off with DPMS on suspend?
USE_DPMS=true

# Use Radeontool to switch the screen off? Seems to be needed on some machines
# RADEON_LIGHT=true

# Uncomment the next line to switch away from X and back again after resume.
# This is needed for some hardware, but should be unnecessary on most.
DOUBLE_CONSOLE_SWITCH=false

# Set the following to "platform" if you want to use ACPI to shut down
# your machine on hibernation
HIBERNATE_MODE=shutdown

# Comment this out to disable screen locking on resume
LOCK_SCREEN=true

# Uncomment this line to have DMA disabled before suspend and reenabled
# afterwards
DISABLE_DMA=true

# Uncomment this line to attempt to reset the drive on resume. This seems
# to be needed for some Sonys
# RESET_DRIVE=true

# Add services to this list to stop them before suspend and restart them in
# the resume process.
STOP_SERVICES="networking"

# Restart Infra Red services on resume - off by default as it crashes some
# machines
RESTART_IRDA=false

# Switch to laptop-mode on battery power - off by default as it causes odd
# hangs on some machines
ENABLE_LAPTOP_MODE=false

# Spindown time on battery
SPINDOWN_TIME=12

Vous devez également modifier dans /etc/X11/xorg.conf la partie concernant la carte graphique.
La partie concernant la carte nvidia 8400gs avec les drivers propriétaires fournis dans Ubuntu Hardy est ainsi :

sudo cp /etc/X11/xorg.conf /etc/X11/xorg.conf.bak && sudo gedit /etc/X11/xorg.conf

Section "Device"
    Identifier     "nVidia Corporation G80 [GeForce 8400M GS]"
    Driver         "nvidia"
EndSection

Section "Screen"
    Identifier     "Default Screen"
    Device         "nVidia Corporation G80 [GeForce 8400M GS]"
    Monitor        "Écran générique"
    DefaultDepth    24
    Option         "RenderAccel" "true"
    Option         "AllowGLXWithComposite" "true"
    Option         "AddARGBVisuals" "True"
    Option         "AddARGBGLXVisuals" "True"
    Option         "OnDemandVBlankInterrupts" "True" # Optimisation
    Option         "Coolbits" "0" # Passer à 1 pour permettre l'overclocking, à vos risque et péril !
    Option         "TripleBuffer" "true"
    Option         "NoLogo" "True" # Pas de logo au démarrage
    Option         "RandRRotation" # Rotation de l'écran avec la commande xrandr -o left par exemple
    Option         "NvAGP" "1" # Résout problême d'hibernation
    SubSection     "Display"
        Depth       24
        Modes      "1280x1280"
    EndSubSection
EndSection

Section "Extensions"
    Option         "Composite" "Enable"
EndSection

Regarder les commentaires de celui-ci, je n’ai pas tout détaillé.

Avec ce xorg, compiz fonctionnel, pas de problème de mise en veille / hibernation, rotation de l’écran avec xrandr possible !

En espérant que ça vous soit utile !