Wow so many different opinions, looks like I will just have to experiment to see what suites me. Thanks to all
While there are many opinions on it, the concept of lighting behind a display is tested and proven. The idea is that if you introduce a properly calibrated 6500K light source behind the display then it will help the overall appearance of the display.
Logically:
If the room is pitch black, then anything on screen that should appear as black, but isn't because of the display technology in use, will appear glaringly NOT black.
If the room is dark, then your eyes will have to deal with a significant amount of contrast in your field of vision from the dark room, to the bright display. This can cause eyestrain and headaches.
If the room is colored differently, or has lights on that are not 6500K then the colors on the screen can seem inaccurate when they are, in fact, dead on. The 6500K light source helps your eyes adjust to an accurate color level and will enhance color and image quality that is seen.
The shifting colors of Ambilight is most definitely a gimmick that most people find distracting. While some may like it, it actually will end up fooling the eyes in a way that will typically make an image on screen look worse than it actually is.