There were a whole lot of questions being thrown our way about what the hell the difference is between article spinning and article rewriting. See, the new ChimpRewriter was being labelled as article rewriting software instead of article spinning software.
In short, article spinning is generating multiple copies of some content, and article rewriting is rewriting it once.
Spin when you are are doing off site promotional activities on Web 2.0 and directories.
Rewrite when you are writing money/main site content, and do NOT do it automatically. Just like you would write an essay.