I've been staying off of the Pro-2A boards for a while now, but this sort of thing gets debated a lot there. I think it was mentioned above by scottwww that we'll never truly have the full story, and should take that into account.
My understanding, IANAL, is that in PA, public servants have no expectation of privacy. Hence, why you don't need a cops permission to record him (audio or video). I don't want to be a test case, but that's my understanding.
I've only started the recorder on my iPhone once during a traffic stop. The cop wanted to disarm me and was upset that I didn't mention to him that I was armed when I was confronted with the question, "Do you have anything I should know about in the car?". I didn't, so I told him no. (PA has no duty to inform - only if directly asked about it). He confirmed in the recording that in fact was how he asked the question, so it's not like he could claim that I lied about the firearms.
I started the recorder, we waited while a Sgt. showed up. The Sgt. basically told the cop to stop trying to make mountains outa mole hills and I went on my way with a warning to slow down. I was by myself and had nothing to do that day but mill around. YMMV.
One Pro-2A group I used to be active in even had a community voicemail setup so that older folks who might not know how to activate their phone's recorder could just dial a number and let it start recording. Some good things came from that for the people of PA.
Like I said, I have no interest in being a test case for some of the bogus stuff that LEOs do... But, it's gotta be helpful, if you're in the right, to have that kind of data in court. Remember, they lied when we beat them up in gym class too...