Plagiarism is wrong. When I was growing up, there were those who plagiarized papers, etc, from previously published texts. This involved finding the texts through library research, and copying out the passages that were needed.
The problem is, now we have the Internet. Copy-and-paste technology just made plagiarism a whole lot easier. Over at This Fish Needs a Bicycle, she's learned that two bloggers are copying her content, and urges us to overwhelm them with electronic reprimands. See this post to see how Fish wants us to help.
Be vigilant about protecting your own content. Post a copyright on your online material, and from time to time, check this website to see if you're being plagiarized.