It's for the 1.8 petrol and up and I believe all diesels have the option.
The system has a hydraulic steering pump augmented by an electric motor. The amount of extra assistance you get from the electric motor depends on the mode (and speed - faster you go, the less help it gives you).
Comfort = maximum assistance for lightest steering
Normal = electric steering at 50%
Sport = no electric assistance - gives most feedback through the wheel.
The electric steering can feel a little numb.
Personally, I run it in Sport. The steering isn't that heavy (and I'm a fairly big bloke who can cope lol). I like the feel of knowing I'm connected to the front wheels. Used to have a Mk2 Punto with electric steering and wasn't overly keen on it.