Here is a link to the Library of Congress' website on copyright law.
http://www.copyright.gov/
As a professional writer, I have a few concerns. First, if someone used any of my work without permission, I would sue, regardless of whether I expect to receive compensation. A lawsuit can also make the user remove the information or otherwise stop using it, which may be enough for me, or any other writer, to sue.
Secondly, when you use someone else's work, you are accepting it at face value. Do you know if the information is accurate? Do you understand the information well enough to rewrite it and not create an error in the information? I have interviewed a lot of people and there are times when I repeat what they have told me as I understand it only to have them tell me what I have said is not quite the same as what they said.
Something that happened several years ago comes to mind. A woman who was working on her master's thesis at Harvard or Yale or one of those Ivy League colleges used material she got from a website. The website turned out to contain lots of information presented as fact that was basically made up stuff from a delusional person.
I would hesitate to use work I couldn't vouch for, especially if I had no way to determine reliability of the source.