Comment 4 for bug 43525

You can disable suspend/hibernation using gconftool
http://live.gnome.org/GnomePowerManager/FAQ#Why_does_GNOME_Power_Manager_not_let_me_suspend_or_hibernate.3F

AFAIR, you should also be able to disable it now in gnome-power-manager.
See http://commons.oreilly.com/wiki/index.php/Ubuntu_Hacks/Mobile_Ubuntu

Also note that acpi-support is being deprecated:
https://wiki.ubuntu.com/AcpiSupportDeprecation