Its definitely worth it. The buyback process is very easy. They offered me a lowball cash settlement first to keep the car and when I declined, they came back with the buyback deal. Your doing BMW a favor by not lemoning the car AND your saving yourself the 7-20% attorney fee. I posted awhile back how they figure the buy back price. If its something you're considering do some searching and see what others on the forum got. I know it works differently on leases, but still a good deal.
Sorry for going so far off topic on an excellent thread. I love my 'is' and plan on keeping it for a while, but if you have legitimate issues with you car, it should be handled properly. It appears BMW isn't effectively handling issues with these engines.