One of the owners of the local BMW dealership is an interesting fellow. Among other things, he is a retired navy admiral who was in charge of the development and training programs for the F-18 Hornet jet fighter. He also has an advanced degree--PHD, I believe, in engineering of some sort. Anyway, one of his projects for his degree involved a study of oil for motorcycles. After nearly a year of research he concluded that any oil specified for use in a diesel engine works well in any 4-stroke motorcycle engine. He recommended using Shell Rotella-T 10W40 oil in my bikes.
What I've been using, however, is Castrol ActEvo 10W40 oil. It's a dino oil with "synthetic properties" whatever that means. The guy at my local Honda dealership service dept. recommends the ActEvo. You can get it on sale at Cycle Gear stores for $3.99 a quart--that is if you have one in your area. Otherwise, the Rotella-T is great stuff. As far as BMW's in concerned, BMW specifies 15W50 oil for their bikes. IOW, you don't necessarily have to use motorcycle-specific oil in your bike. I do change filters with every oil change, however, at around 3K miles.