Comment 38 for bug 338328

Instead of blacklisting the video module, I found a new workaround:
  $ echo "options video brightness_switch_enabled=0" | sudo tee /etc/modprobe.d/video.conf
This again gives me 10 levels of brightness on my laptop instead of just 5.

I wonder if the video module can special-case some hardware configurations, so that brightness_switch_enabled is false for them by default. It appears to contain some list of Acer Aspire models, but not mine:

# strings /lib/modules/2.6.32-24-generic-pae/kernel/drivers/acpi/video.ko | grep "Acer Aspire"
Acer Aspire 5720
Acer Aspire 5710Z
Acer Aspire 5315
Acer Aspire 7720

# dmidecode -s system-product-name
Aspire 5920G