I believe I had the same problem as you, the computer resumed from suspend but did not turn on the screen. I found out the culprit was fgrlx. Disabling it and using the radeon driver instead made suspend work for me.
enrico,
Your instruction confused me a little. Adding "acpitool -W 16" into /etc/rc.local has the exact same effect as adding "echo "LID" > /proc/acpi/wakeup". Adding them both makes them cancel eachother. So I would just stick with b3nn0's suggestions, that do the trick for me.
gaelfx,
I believe I had the same problem as you, the computer resumed from suspend but did not turn on the screen. I found out the culprit was fgrlx. Disabling it and using the radeon driver instead made suspend work for me.
enrico,
Your instruction confused me a little. Adding "acpitool -W 16" into /etc/rc.local has the exact same effect as adding "echo "LID" > /proc/acpi/wakeup". Adding them both makes them cancel eachother. So I would just stick with b3nn0's suggestions, that do the trick for me.
Best,
Mateus