I started having the same problems. The display does not switch off anymore after idling. Any new ideas on how to solve this? Gconf? Some ini file?

No idea whether this is related but I updated the maps in Maps application yesterday. The update seemed to leave the screen on. I manually switched the screen off with the power button but when I unlocked the phone again, the update and Maps had stopped. So I had to update again and leave phone unlocked and let it update. So could this update have left my N9 in some invalid state?

Thanks already for the answers!