Just got a new mid-09 uMBP 15", I don't think that the ambient light sensor is put at a right place - now, with the ambient light sensor put next to the web cam, the keyboard illuminates as long as the ambient light sensor is not DIRECTLY towards light source. 
Is it OK to just leave the keyboard illumination on? what's its lift span? If it's the same as the LED backlight, then I don't care if the keyboard illumination is on or not.
Is it OK to just leave the keyboard illumination on? what's its lift span? If it's the same as the LED backlight, then I don't care if the keyboard illumination is on or not.