Five years ago I was teaching a literature class and had the students review a novel for their final project. I remember allowing them to search online reviews and discussions if they needed additional insights. What I got was a significant number of students submitting cut-and-paste reviews.
I found out because a lot of them were written in near-perfect English (a facility that the plagiarizers didn't have) and because a couple included the book prices and availability information from Amazon. I went ballistic on the school's yahoogroup (it was, and still is, a small school) and failed every plagiarizer on sight.
I still automatically fail anyone who submits cut-and-pasted work.
I also wrote this.