Some people think that if something is given away free, that they can do whatever they want with it.  The courts ruled recently that copyright law for software does cover software that is given away free.  Usually, that software comes with restrictions such as giving credit to the original author and limiting the kinds of changes that can be made.  The courts are now saying those restrictions are binding.  The same is true for just about anything else.  Just because a printable copy of a famous painting is online doesn't mean it's OK to make posters of it and sell them.  Just because you got a free sample of toothpaste in the mail doesn't mean you can break it down chemically, then whip up a batch and sell it as your own.
    In the blogosphere, it is a common problem.  I have visited some blogs where it looks like every story was copied word for word from someone else's blog or web site.  That is wrong and illegal (It also makes for a pretty boring blog).  If you see a story on another site you like, link to it, don't copy it.  If you like the idea of the story, but not how it's written, then write your own story on the subject, don't just copy someone else's.