I had two Vauxhall Omegas - one (R-reg) for 4 years, the other (Y-reg) for seven years - which did a combined mileage of 80k. Both parked in the street and never had any rust issues.
Both were generally reliable, and I never broke down - though some things did go wrong and were dealt with under warranty. So in general reliability was not abysmal, but not spectacular either. Yes I would happily buy one again if they still made them - i.e. large RWD 5-seater saloon - but the FWD Insignia has no real edge over the Saab for example.
My MB - 06 plate - seem to have had so far only four minor issues, so on balance far more reliable than the Vauxhall.
On another note - I always thought that modern cars are made based on the assumption of a 7 years life cycle - 10 years seems a bit long. This is encouraged by governments because the car industry will die if people did not upgrade often, and if older cars did not go out of circulation sooner (see scrappage scheme).
In reality, the life span of a vehicle is only partially affected by it's built quality - it is mainly affected by desirability. MBs are desirable cars so keep their value better second hand - especially the diesels - and will be worth repairing. Astras, Vectras, and Omegas depreciate like a free-falling lift, so at 6-7 years even a minor engine fault will deem them uneconomical to repair. My 7-years old Omega was sold with 50k miles on the clock and very well maintained, including 4 brand new Michelins to the tune of £600, and some £100 left on the tax disc - but fetched only £1k in trade-in, as no one wants a thirsty previous-generation V6 Omega averaging 22mpg (the 4-cyl and diesels kept their values better). It probably ended retailing for £2,500 after some serious valeting and minor scratch repairs. But even so at this value, a rather small engine problem will scrap the car.
A similar-sized 7-years old MB (C/E-Class) is still worth at least £5K-£6K even for the most basic models, so will be worth repairing.
Incidentally, I was shocked to see the other day a lorry with scraped cars piled on it, one of them was a very clean and healthy-looking Astra Van with 04 plates - and it then dawned on me that at 7 years old if the cambelt snapped the car goes to the shredder.
So how long a car lives is not simply a direct result of its built quality - but more of what people are willing to pay for it to keep it on the road.
