All Apple notebooks, except for the Powerbook G3 Series (Wallstreet), do this. Perfectly normal.
The Wallstreet glowed slightly, only because of backlight leaking to the logo. All the others are illuminated by design. There's a piece of translucent white material between the logo and the back of the display.
I wouldn't have it any other way. Nothing like my entire family and a couple friends, all sitting around the living room - picture a semi-circle of glowing Apple logos. 😎 I've also seen my local coffee hangout aglow with Apples. Usually, at this shop anyway, about a 6-1 ratio of PB/MB to wannabes 😉