Just drive it and leave it in D.
The intelligent CVT will alternate between S mode and D mode automatically according to driving condition.

No harm to the gearbox while driving with 7 speed mode, although you will be changing gears less effective than the computer.

In D mode,and on normal driving on flat road, it will maintain at lower RPMs than S mode.
In S Mode, the gearbox allows the engine to maintain it's rev higher than D mode.

Example:

100KM/h

D Mode = 2200RPM
S Mode = 3000RPM

Usually the gearbox will auto detect the gradient (uphill and downhill) and alternate between D and S.

And yes, 7 speed mode is a "simulation" of a '7 speed gearbox' with all the 'gear changing effect' and revs go 'up and down' like a normal gearbox,
rather than "constant" RPM.

Yes. Though it's not mentioned anywhere in the brochure or even the manual, it is built into the ECU.

For example, i am driving 110Km/h at downhill of gua tempurung PLUS highway, the moment I let go the gas pedal, the gearbox will downshift to lower ratio gear, the RPM goes up, and I can feel some engine braking.
Conventional auto gearbox will continue to be in 4th gear/Overdrive and you can feel your car going faster and faster (like a runaway roller coaster effect)

Do the same thing on flat ground road surface and the gearbox maintains the same RPM.But if the road has a slight slope, it will rev higher (according to road gradient and your gas pedal pressure), as against to conventional gearbox which cause the engine to "struggle" in the wrong gear.

Go uphill Genting/Cameron, and the car will maintain RPM at higher rev (automatically switch into S mode, even with gear in D). Don't need to even floor hard to get the gearbox "kickdown". Just drive like normal.

See how complicated? City owners will know what I am talking about.

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Added on December 25, 2009, 10:53 am

If you put in S mode, then it will hold the revs at higher RPM from 0KM/h right up to maximum RPM and maximum top speed. It will hold at higher revs until you change back to D.