It doesn't happen often, but I've had a couple of situations while out taking pictures of being stopped by a rent-a-cop and told that what I was doing is illegal. This led to a lot of research and a printed copy of Andrew Kantor's "Photographers Rights" being in my gear bag at all times. Yesterday, while I was out at Greystone Park Psychiatric Hospital, I was stopped by a real policeman and asked to stop. The big difference between the experiences with pseudo-cops and this one was that he was so much cooler than they were. No shrill "you can't do that" and demands that I delete (which I don't do, because it's not a requirement without a court order) or being followed while my camera is obviously capped, but rather he was helpful and even told me that if I contacted the main office, I might be able to get permission for a shoot. He was just a heck of a lot easier to contend with and even spoke a bit about being a hobbyist with a camera, himself. He mentioned that he felt that the building wasn't a good subject, because it was ugly and boarded up. At that point, I smiled, raised an eyebrow and said;
"Not all photography is about beauty."
He sort of eyed me for a moment, with a look that said he thought I was crazy. The fact of the matter is, while I do tend to take pictures of flowers and the like, there are other things that make for interesting pictures. There have been a couple of times where I've seen old buildings, which were clearly once magnificent but have fallen victim to urban decay and they fascinate me. Greystone has the added factor of interesting and infamous history. I will most definitely be calling to ask permission, and if I get some decent shots, I might even make them Creative Commons and give them to Wikipedia, as the current shots there are less than optimal.
Further pictures can be seen in my galleries under Greystone Park Psychiatric. They aren't great, as I was stopped before I could get that "just right" picture.