same issue here
I have the same issue in my Macbook Pro 13" (Summer 2009). Display usually dims and turns off the backlight keyboard as well, in spite it is set to never turn off. No matter how many times or ways you set and reset and change the preferences and so on... It still keeps on doing it. Sometimes, your efforts make some difference and you see a change in the behavior of the backlight, but when you think you have solved it, it happens again... Very ironic. You can reset SMC and/or PRAM, reinstall latest Mac OS X updates, reboot, but it still keeps on turning off over 2 minutes of inactivity, and it is set to never. I know it is a system issue, because it happens too if you try creating a new account to see the results. But in my bootcamp partition it's ok, the backlight keyboard and the display dimming obey your preferences, don't play with you
So, it hasn't got any relation with preferences.plist, powersettings.plist, bezelservices.plist or whatever.plist in system or user library, because I've tried everything after reading every thread and discussion, forum and tip to solve this issue without success.
There are a lot of people with the same problem or, at least, with other anomalous behavior on the display dimming and/or backlight keyboard...
Does anyone know anything new about this issue?
I hope they solve this as soon as it's possible.