* These days, almost all things are copyrighted the moment they are written, and no copyright notice is required. That means that EVERYTHING, even stuff you find on Google, Ask.com, etc is OWNED by someone!
* Postings to the net are not public domain, and don't grant you any permission to do further copying except maybe the sort of copying the author might have expected in the ordinary flow of the net.
* Fair use is a complex idea. It is meant to allow certain valuable social purposes. (Like some educational uses). Ask yourself why you are republishing what you are posting and why you couldn't have just rewritten it in your own words.
* Copyright is not lost because you don't defend it; that's a concept from trademark law. Anotherwords, if you don't go to court because someone uses your one-page report and puts their name on it, you do not lose the ownership. It is still your paper, PERIOD. The ownership of names is also from trademark law, so don't say somebody has a name copyrighted. A name is trademarked. Also a log is trademarked. For example, NIKE is a trademarked name. The logo checkmark for NIKE is a trademark too.
* Fan fiction and other work derived from copyrighted works is a copyright violation. (For example, a Tabloid (fan fiction) uses something from a book.. they don't ask permission to say somethhing thats written in the book. That is illegal.
* Copyright law is mostly civil law. (That is where the special rights of criminal defendants don't apply). Watch out, however, as new laws are moving copyright violation into the criminal realm. Copyright laws are changing as the internet becomes more a part of our lives.
* Don't think that you are helping the copyright holder by using their work; often it's not that hard to ask permission. For example, I may say that by using your song it helps you out. NO..it is illegal to use the song for any reason unless you tell me it is OK for me to use it.
* Posting E-mail is a violation. You can not put an email someone else wrote out there without their permissin. But revealing facts from E-mail you got isn't illegal. I CAN say that Susan said Joe is getting his hair cut if that was in an email she sent me. I CAN NOT hang a copy of her email in the hallway for all the school to see. For almost all E-mail, nobody could actually sue you for posting your email. The law doesn't seem to do much to protect "intellectual property" with no commercial value (commercial meaning it is not for sale).
Our county developed a nice copyright page for teachers and for general information about copyright issues. There are questions and answers here that you may find useful.

Source: http://www.templetons.com/brad/copymyths.html