I felt a little uneasy reading this in the article. I write CS conference papers that are all in the same area, so obviously, some of the background information (which is a pretty small part of the overall paper) is basically copied from paper to paper. And that part is the most polished.
I don't feel uneasy because I'm doing anything remotely unethical---I'm not. I feel uneasy because it sounded a bit like the description in this article was over-broadly defining self-plagarism.