I don't have my ipad 4 yet, but the icons thing sounds perfectly normal. You see things like this with PC's - basically the graphics driver switches modes for different tasks (movies, 3d games etc). When you drop back to the home screen the GFX chip is just redrawing the icons in the correct resolution. I might be wrong, but this is what you describe sounds like.
As for the backlight, what you are describing sounds like a phenomenon known as 'floating blacks'. It can be observed in many TV's and is better/worse I some TV's. Can be annoying is cheap TV's but can usually be rectified with a software update, depending on the cause.
To your first paragraph, I know what you're talking about, but that's not what this is. It's a byproduct of the floating blacks. What is happening isn't just a backlight adjustment in movies, it's a contrast adjustment. Then, if you happen to close the app during those contrast bump, you're left staring at a homepage of icons with contrast out of whack until it fades back to normal.
Again, that the icons look messed up for a few seconds is far from a big issue. It's notable, sure, but not worth crying over. What is far more frustrating (fatally so, in my book) is that the floating blacks are all too aggressive. Once again, for those who didn't read my first post fully - the fact that I used this trailer and the use of the PAUSE button on one particular shot is just a quick and easy way for anyone with Internet to test this phenomenon.
For the rest of us, just watching a movie with a dark scene will result in the floating-blacks issue every few seconds.
So, once again, the home-screen distortion is just a BYPRODUCT of the movie-watching issue. The movie-watching problem is the thing I'm concerned with.
I spoke to a senior advisor at Apple, and he's seen/understands exactly what I'm talking about, so hopefully iOS 6.0.2 addresses it.