I have nothing to hide, but don't care to be tracked. If information is anonymized, I'm ok with that. But there is no good reason for there to be a database of my location at all times. There should absolutely be an opt-out option for those iphone users.
Yeah the opt-in thing I can agree with, and yeah it is anonymous. No one is going to figure out where you specifically were by looking at that data. I believe Apple said they are going to include an opt-in choice in their next OS version (someone correct me if I'm wrong).
Either way is fine for me...I don't care if they track my phone, because I don't have some false sense of privacy or security. You'd be surprised to know the actual lack of privacy that exists in the world regardless of your mobile phone. if someone wants to know where you are, they'll eventually find you, especially if you're online in anyway.