Just came across this post at Dick Margulis' blog. It is a very brief, very lucid explanation of the issues involved in copying text without permission. I recommend it if you have any questions at all about the difference between "published" and "public domain," Fair Use, or whether you need permission to use material that you've "found" on the Internet or in offline sources like books and magazines. Dick is a publishing professional and he's done an excellent job of summing up the sometimes confusing and often contentious issues involved.
I expect that most people reading this already understand these issues, but it doesn't hurt to review them. And if you have a blog, why not direct your readers to http://ampersandvirgule.blogspot.com/2007/07/mine-and-thine.html? It would be a nice public service.