This is my two cents' worth: I have been using the BBlight application since it was first released; I absolutely love it for its indespensible value.
The BBlight settings allow you to set it up so the backlighting activates when you unholster the Blackberry, and/or when you push any button, and/or when external power is being supplied, and/or at a certain time of the day, with a selectable duration period.
This application is a must-have if you use your Blackberry while driving, especially at night!
Here's the webpage where you can download the various BB applications. http://sourceforge.net/projects/blackberrytools/