Palms never got this feature, but many Pocket PCs did. I remember that my HP Jornada had a light sensor at the top so that it could automatically control the brightness of the LCD screen. Well, the Treo can have this feature to, thanks to the camera and a new application called Brightcam.
Brightcam is a simple application that checks the light level of your enviroment everytime you turn on your Treo. If Brightcam detects that the Treo is in a dark enviroment, it automatically turns on the keyboard's backlight and dims the screen. It is a freeware application, available now at Palmgear.
The developer, TreoCentral user JFMw, has a thread in the TreoCentral forums were users are discussing new features and bugs in the application. Please post any comments there for Jean-Francois to read.