I just started working on this rewriter today, but it already is yielding 5%-10% changes to large articles. It does best on finance based topics. I will be constantly changing it and making it better. Eventually I will turn it into a wordpress plugin and a cURL website post plugin script to have it rewrite blog posts directly from the blog itself. Here it is, try it out: http://bright-tutorials.com/articlechanger.php
I just used it to check how it performs though it shows me 31 or 8.83% but still it doesnt passes the plagarism test and copyscape... though the quality of article is good and readable
I didn't find it very good, entire paragraphs of a 1500 word article were left unchanged, and it only changed 63 words from those 1500. Make a new thread when the script works better as I think it would be extrmely good if done well. Good luck.