This week the local paper had a short piece on the Dee Brown case. Brown is a former Raptor player. I think currently working in the front office of the Magic. A few years back he was pulled over. The officer claimed he had good reason to pull him over and it wasn't because he was a young black man in an expensive car. Well turns out when he found out who he'd pulled over and that it was going to court the officer embellished his notes. The defense lawyer was able to prove this and the appeals court upheld it. The scary part was when he was questioned about it.
The lawyer was asked something like this " So this is a good thing. The police won't do this again?"
Lawyer " No they'll just figure out a better way to cover it up"
The fact you are within your rights doesn't mean much. Never really did. The question is how much hassle are you willing to put up with? In the end even if you are cleared many will believe you got off on a loop hole.
The point about asking permission? I'd say never. Asking lets them say no. No is the safe answer. If they come over to hassle you just be nice and smile. Odds are they'll think you're not worth ruining a good coffee break over.
I found the post about the cops targetting photographers at demos interesting. Here they tend to love them. Gives them photos and videotape to seize later and use in court.