Interesting that you should mention the rear seat area rattling. I was on a trip this weekend and noticed a new noise coming from the rear seat area that I could not pinpoint. I will check the dome light.
They tried to cure my dash noises by foam taping everything. That didn't really work, so when the dash started to crack around the airbag, it was replaced, twice. This seemed to cure the centre dash rattle. I now have a new noise that seems to be coming from the dash, passenger side around the vent area. I have yet to have time to fix, but I will let you know.
The passenger door has also developed what I would call a "flapping rattle" type noise. I can stop it by pressing against the aibag area, but it is tough to drive like that. I will be taking the door apart ASAP.

After my seats were replaced, they no longer squeak at all.

I also had an exhuast rattle that was caused by a bracket that had warped (front of exhaust, behind the cats). It is placed between the exhaust pipes and appears to hold them together.

I think a little more testing needs to be done before MB rushes to launch these new models. I waited a year and a bit before buying a CLK in hopes to avoid some of the new model glitches (not that MB should have them anyway) but no such luck. A had intended on getting a CLK55 or E55 next, but now I am hesitant. I guess my problems may seem minor, but I expected a lot when I bought a new MB (and shelled out a LOT of hard earned $$) Maybe I expected too much ??