One of the frustrating things about netbooks is that, because they're cheap, you usually miss out on premium features like backlit keyboards. Of course, because they're cheap owners often feel happier with the idea of opening up and generally hacking them, and that's just what My Dell Mini forum member vrg3 did to his netbook. Wanting to still be able to type while in the dark, he drilled a hole for a white LED up by the A90's webcam, which is toggled on and off via the Ctrl key.
He describes it as the DIY version of the Lenovo ThinkLight, and it uses an LED salvaged from a string of Christmas tree lights together with a ATTiny13 microcontroller. The latter monitors the Ctrl key via the keyboard pins; hold down the button for a few seconds and it switches the light on and off.
Of course, if you're feeling less confident about microcontroller programming then you could rig up a switch or button somewhere instead, though of course that would probably require more holes cutting in your netbook. While the photo above doesn't look dramatically impressive, according to vrg3 that's the fault of the camera rather than the performance of the LED itself.