Well, I have spent several hours researching into this and I believe that I have found some real good guide lines.
There are three sources I would look at when looking at this subject.
1: http://www.kantor.com/blog/?s=photography+rights
2: http://www.usatoday.com/tech/columnist/andrewkantor/2006-08-11-photography-rights_x.htm
3: http://www.krages.com/ThePhotographersRight.pdf
The first link has a PDF file worth reading. One and two are written by the same person, but have very good information.
The guidelines are this: 1. From property that is considered public, you can take any picture you wish. To clairfy, this means from a sidewalk, park or any other area.
2. Although you may take pictures in a public place, such as a mall, you may be asked to leave, there by creating a trespassing charge.
On this second one, there were many, many opinions on this subject, of how can you one minute be allowed somewhere and the next be trespassing, but that is another story. The simple answer is indoor malls, it is legal to take photographs, even without the permission of the owner.
Military bases and government buildings, and certain types of infrastruction is another question. New York has a law that states it is illegal to photograph the bridges. Everywhere I read states that bases and government buildings may not be legal either, but it may be as well.
This I know, I was always told to report any photography to the military police when it was observed on base. Is that so that the appropriate authorities can investigate... probably. My Oklahoma Courthouse story above is a good example where they ran my name and checked me out, but released me. I was polite, I explained what I was doing, no problems.
I have signed in to go into several military bases to waymark. I didn't tell them that, but I went specifically to "public" areas. Cemetaries, historical markers, historical buildings, static displays of equipment (not in use), and museums. All of which I did not have a problem photographing, either ethically or with the authorities. The front gate does send up warning bells for my ethics. It is part of the base's primary line of security. In posting for that category, I will no longer post, if I can not find the welcome sign without comprimising the security of the installation.
The one overriding factor that I found of interest is in publishing photographs, which is of particular interest to us since that is what we do. Deflamation is illegal, so that picture of the Little Caesars dude scratching himself can not be posted, even though it is funny. I would say a lot of the pictures we see floating around on the internet could fit into this. It makes how we approach "funny signs" a little different if in the Wendy's billboard it says Now Hiring all Shifts, with the "f" missing from the last word.
And finally, as far as I am concerned, I am not going to jail nor going to embarass myself or Waymarking.com over taking a photograph. You attract a lot more bees with honey, and I will remain polite, as I would recommend to everyone.