I came across a "Protected by Copyscape" banner in a writer's blog and was curious enough to check out the service. From their About page:

Copyscape is dedicated to protecting your valuable content online. We provide the world's most powerful and most popular online plagiarism detection solutions, ranked #1 by independent tests. Copyscape's products are trusted by millions of website owners worldwide to check the originality of their new content, prevent duplicate content, and search for copies of existing content online. Copyscape provides a free service for finding copies of your web pages online, as well as two more powerful professional solutions for preventing content theft and content fraud.

I've heard mixed reviews about this service -- has anyone used it? I tried it with pages from my site but didn't have much luck because of my site layout: because I have navigation sidebars that repeat throughout the site, Copyscape kept picking up that text so the results always gave me my own site pages. I was using the free service, however, so was only seeing the first 10 results. Anyone else have luck using this service?