I'm a mechanic and we've sold quite a few S' from work.
If you're getting one with the low profile tyres the road noise is horrible, it almost sounds like all 4 wheel bearings have failed and the steering needs constant correction to keep the car in a straight line.
The chains give huge problems with stretching, although this is normally caused by low oil levels in the engine due to the oil consumption being ridiculous.
BMW say a consumption of 1 litre per 1000 miles or so is acceptable. So you will have run 12 litres through it between services.
The gearbox's and PAS pumps have been upgraded on the later models so they shouldn't give you any problems.
Oh and don't be fooled into believing that because it's German that it will be reliable. The days of German engineering being king are long gone. They're just as shit as everything else now