I followed all the steps in this guide: https://help.ubuntu.com/community/MacBook5-1/Intrepid
I was able to fix the sound, keyboard multimedia keys and enable some temperature and fan sensors.
What still doesn't work:
- Adjust screen brightness.
- Show battery status. I tried resetting the SMC controller btw. Apparently Ubuntu thinks there is no battery present.
- When I try to shut down or reboot, it stays On with a blank screen.
I am still booting with the acpi=off line, otherwise it won't boot.
UPDATE: Apparently the shut down and reboot issue is fixed by installing version 180 of the Nvidia graphics drivers. Will try later.