Change intervals
BMW changed their oil filter design last year because they found they weren't holding up under the extended drain intervals. So how many millions of people ran extended drain intervals with deteriorating or inefficient filters?
Also, you can find discussions from BMW techs on E46 Fanatics that question BMW's extended interval plan. They don't think it's such a good idea to go for so long, and since BMW has a vested interest in you running with these long intervals (maintenance included in vehicle purchase), you can't believe that they have your best interest at heart.
On top of this, you'll find people who think Castrol Syntec, BMW's current oil of choice (was Valvoline up until a few years ago), to be a "quasi" synthetic oil that uses conventional oil as a base stock. Mobil took Catrol to court over their use of the word synthetic in reference to their Syntec oil, but lost because the ASE has no real definition of what synthetic oil is. I could grab a quart of Valvoline off the shelf, drip a drop of teflon into the bottle, and sell it as synthetic. The word has no real meaning and Castrol has taken advantage of this fact to sell oil that the rest of the industry recognizes as inferior.
So you can trust BMW or you can invest in some inexpensive insurance and change your oil more often. When the engine siezes up at 150,000 miles because of oil related issues, BMW will not be returning your phone calls.
I changed my oil at 1200 miles after break-in, plan on changing it at 7500 miles and will take it to the dealer at 15000 miles for my scheduled change. Then I'll change it every 7500 miles after that. I'll be using Mobil 1 exclusively, even when it goes into the dealer.
If you don't want to change your oil this often, spend $5 every 7500 miles and change your oil filter. It's on top, so you don't need to drain your oil to get to it. It's very cheap insurance.
--gary