Firstly, with regards to his actions outside of private properties, how are his actions any different to say, a journalist stood with a camera with a long range lense taking pictures from the highway to the office? The invasion of privacy is still clear, the only real difference is the knowledge of the situation.
After having security cameras follow around our every move (I live in the most widely covered town in England) we have become numb to it, it has just become a part of every day life to expect to be stalked by the police and other entities. I believe the uncomfortable feelings these people experienced were due mainly to the fact that he was also though, but that alone would not make them uncomfortable, if say, for instance he was stood in the street taking a video of nothing in particular, say, the other side of the road, people would happily walk by him with little or no discomfort.
The point where he started "invading privacy" by following people round is where they began to feel uneasy, being followed by a camera man is unnatural, but I beg the question, how is this any different to paparazzi? How is this any less legal, say, they the topless photos of Kate Middleton, following Lady Gaga in to a hotel to get some exclusive shots or taking a photo of Madeleine McCann's parents while they are in their home?
The legality of this is in question by a few of the posters, but I feel this is totally wrong, it should not be the legality of whether or not to record audio, or whether the video can persistently track you, it should be a question of free speech versus privacy.
On the one hand you have an annoying man who isn't doing any genuine harm, on the other hand you have a person who clearly believes their privacy is being infringed, the question is, to whom do the majority of the rights fall.
I'm no expert on American laws, but from what I know, freedom of speech is protected by the first amendment, and you could argue that if he is trying to change peoples views and mentality with this video, it is in fact a form of speech and should be afforded the same rights, though a general exclusion is invasion of privacy, according to the Wikipedia page regarding the first , but if so, why is a security camera not an invasion of privacy?
I would be willing to bet a significant portion of this months wages that even if he followed suit with the security cameras and removed the sound from his recording, almost every person would still have felt uncomfortable, especially in the UK, where legally, unless you are suspected of having committed an illegal activity, a hand operated security camera can not track you for more than 5 seconds. 
 - If indeed, the right to not be on video while in public should be regardless as privacy, can you truly have privacy while in public?
 - http://en.wikipedia.org/wiki/Time,_Inc._v._Hill
 - This number was given to me by an operator of the Blackburn with Darwen CCTV unit several years ago when I took part in a visit for high school and as such I have no proof, so take this point as opinion.
It's an interesting experiment in social norms, but it's not particularly ethical.
The subjects don't know this. Because his behaviour is so unusual, and because he does so little to explain it, it raises questions about his sanity and future intent.
If I get in an elevator with you and start staring at you, I may not be doing anything illegal, but you would be foolish to wait until I actually do you harm before securing yourself.