My 15" Macbook Pro (Early 2011) has always had a problem where when I open the lid to wake it from sleeping the backlight doesn't turn on. I can easily turn it on by changing the brightness, which leads me to believe it is a software problem.
It isn't a huge problem, just a minor annoyance, but I'm paranoid about backlights ever since I had to replace my old MacBook due to a faulty inverter cable which caused the backlight to not turn on.
Update 1: I noticed that immediately after I open it, the screen is still on and it displays the unlock screen, and only then turns off. This was after being closed for only about 2 minutes.