I looked at some previous threads on C vs S.

Clearly the transmition gearing changes are evident as most explain the car will start in 1st rather than 2nd, as well as the rpms reving higher before gear changes etc...

But I found that the car's suspension drove firmer (is this my imagination?)
I looked in the manual and futher back (not in the basic description of C/S) it does say the the selection of C or S adjusts the suspension acordingly.

I'm curious to know if anyone else has felt a difference in the suspension from C to S.

I am still battling a slight vibration felt mainly under the seat, it seems to be less when in S. I am somewhat convinced it is my crappy Continentals.

What year is your car?

Mine (2010 without ABC) has separate controls for c/s suspension (next to comand screen) and transmission (next to comand knob).

I understand that earlier years (2007?) may have combined those functions to one control.

The car sits 1cm lower in Sport mode. It goes down 1cm more above 150Km/h (applies to both modes).

Also, in Comfort mode you start from 2nd gear also in reverse.

Vibrations are not desirable and are caused by tires probably.

Yes, I have a 2007 S550 4matic and I believe they combine both into one button (only one button visible stating C/S) but as Armadillo 888 explained, I guess it does affect the suspension height, I also wonder if it affects the stiffness, as it seems to feel a slight bit firmer.

To answer your question, yes "S" mode does firm up the suspension a little bit. I personally miss the ability to change the tranny and suspension independently like I could in my E550...

S mode firms up suspension yes.. you can notice it above 180Km/h where the normal Comfort mode doesn't feel safe anymore with regards to some high speed maneuvers.

Short answer...
$ vs ¢