I still have the problem (upgraded to 10.5.2 yesterday).
I've tried rebooting, but it's still there.
Do the SMC reset.
The update did not seem to help me.
My backlight keeps turning off to save power I guess but then never seems to turn back on... even in total darkness. Even though I have it set to NEVER on the slider in System Preferences it still turns it off... grrrr.
Is there some way... maybe a command line trick to just disable the MBA from controlling it through the light sensor?
I am happy to just do it all myself with the F5 & F6 keys
I my opinion, the keyboard light should ONLY go off when the MBA goes to sleep. Period!
It is a bit annoying to have it just turn itself off for no apparent reason.
I may try the PRAM reset, but I have no real hope for it.
I LOVE this little laptop, but the backlight really bugs me as I use it a lot at night in dimly lit rooms.
Oh well.
I look forward to any fixes... I am going to try Lab Tick and see if that helps.
I think someone mentioned a program Tab Lick (or something like that) in another back light keyboard thread. That program would do exactly what you want it to do, i.e. keep the back light on all the time except when off or sleeping. If I can find the thread, I'll repost with the program name.