I have always been taught that while in public there is no expectation of privacy.
This is why it is perfectly legal to take a picture of my house from the sidewalk. This is also why it is illegal for me to run naked through the park.
For me this has always been the be-all, end-all of the 'recording cops in public' debate for me.
I mean, bottom line, if he is beating up a hippy in a park then the cop is in a public space.
Now, it is nice to say, 'well he can record me, I should record him!'. But the playground rule 'turn about is fair play!' is NOT a legal standard.
I agree with the majority of people in this thread, I would like to see one of these incidents get to the supreme court. This is the highest order of bullshit.