It's an interesting topic. I read an article about it once... not specifically about BMW, but about Mercedes. Merc and BMW used to have the Prestige market sewn up. But since Audi and VW drove their quality up, and Lexus arrived with their reliability, they all realised they couldn't compete price-wise. Increasingly, cars are now built to a price point, whereas Mercs and BMWs used to be over-engineered. My old E34 5 series was far more solid than my E60. My father in law - who drives like he is in a funeral cortège - recently had a complete front suspension failure (shocks, springs and arms) on a very low mileage CLK diesel. Dealers told him this was normal wear and tear due to speed bumps! I am afraid we are all clinging on to a notion of reliability which was gained during the 60s and 70s for Mercedes and 70s and 80s for BMW... Which just isn't there any more.
That said, BMWs core values for performance based engineering remain the same, and I for one am happy to persevere.
Finally... has anyone else noticed that the 'sixes' seem to have fewer issues than the 2.0 cars? By all accounts that is the same with the E46 and X3 too. Hmmm...