My '10 goes out of warranty in 8-10 months and I've been weighing the extended maintenance and warranty options myself. To me, the extended warranty is just not worth it.
Xcelrrate above says, "The Brake Job @60k miles; front and rear pads and rotors alone was upwards of $4k..." While that's what it was at the dealer, you can buy pads and rotors all around from some place like getbmwparts.com for under $1500. I can install them in half an hour at home. If I don't feel like it, there's a great independent euro shop in town that will do it for a couple hundred bucks. The maintenance is expensive on these cars no matter what, but it's only ridiculously expensive if you take it to the dealer.
And yes, the loaner cars are nice, but for a lot of us the M3 is our 3rd or 4th car. If my M3 melted down today, I'd hop in one of my other cars and continue going about my business. Even if I needed another car, I could pay for a rental with the difference between dealer parts and labor and what it costs at a good independent shop.
I get the peace of mind insurance gets you. And different people have different philosophies on that. But to me, I would rather have the risk of paying for a major mechanical failure than pay a ~$5k "premium."