Had my 8000 for about a month now, and car battery started to die, so had to replace it.  Thought it was interesting what happened after it sat in my car for a bit while I was changing out my battery and had no power.   

When I first fired it up on the new battery, I immediately noticed all my FM presets were gone.   Great, I thought that indicated I lost everything, only to find later that FM and AM presets were gone, but all my XM presets remained.  Also, all my custom theme, audio, LED light settings, wallpaper, and so on remained.    All my bluetooth phone settings also remained.  Then I noticed when I put it in reverse, no back-up camera . . . it was turned off.   When I turned it back on, it lost my custom adjustments to the back-up guides.  I don't get it, why would it lose some stuff and not everything?   

The unit, when shut down, saves the running image along with the registers.  It appears that the presets are not in that saved area -- neither are the camera settings, equalization, subwoofer, speaker balance and similar settings.

The wallpaper and such, along with illumination, is -- and that surprised me as well.