My leased 2007 525i had its oil change as per the idrive service intervals. When I turned it in over the weekend to replace for my new car, I did open up the oil cap and there was no sludge build up that I could see. With 51,000 miles on the odometer, car still sounded and ran perfectly just as I first picked it up 3 years ago with only 10 miles on the odo.
If others want to throw away perfectly good oil and money away by all means go for it, but at the same time don't complain about gas prices being too high

 

Castrol

 

I put on very few miles on my car, especially during the cold months, so I usually just go by the amount of time that the oil's been in the engine. And in my case, I try to change it every 4-5 months. If by some weird chance I put on more than 5-6k miles before 4-5 mos are up (I don't, really - I've put on only 7.5k miles over the course of the past year and 2 mos), I'd change the oil every 7k miles or so. I would also change it myself and not reset any service indicators - just let the iDrive do it's thing...