to keep copying to less than 5 words in a row, unless it´s unavoidable, like the name of a person or place. Otherwise, you may get your story back for a rewrite. Just changing out certain words with synonyms isn´t really your own words, actually rewrite info in another order. Quoted passages at the source must always be copied word for word and attributed to someone.
I am as guilty as any in cutting and pasting parts of articles to offer a point of view. Some of us use extensive cutting and pasting in forums to present a one point or another (usually with quotes and attributes).
I didn´t see the thread that Lois created. I sometimes find myself copying a part of an article because of the information in it that no one will bother to read otherwise, I will have to start watching how much I use from now on. I had figured since I was giving the links to the article it wasn´t harming the OP.
Thanks Ichi for bringing this up, thanks Caution for clearing it up at the same time :-)