And if you're looking for a slightly more scalable solution than "Find a sentence from Page A which is juicy, Google it, record results, repeat for all 10,000 pages on my website", you may be interested in CopyScape.

For example, if you feed them www.tynt.com, they'd tell you that feedmyapp.com has borrowed a few sentences from them. (It makes sense, as the borrowed phrases are part of a listing for tynt.com)