While I've not caught any sites using large block quotes of my reviews I have noticed that where before I posted a review or two there were virtually NO other reviews of the title out there that, several months later, a few sites had reviews that read like paraphrases of my review. Now that's not exactly proof but, then again, when you don't read anything substantially NEW in such reviews it does make you wonder.
For instance I just posted a new review of
Beast in Space, which is only marginally based on my older review of
Beast in Space. But if you click that second link and take a look at the poster at the top of the page and then go Googling for other reviews odds are you'll see that EXACT SAME image. Now I didn't scan it, but I did take the "found image" and clean it up a bit and crop it. Whenever I see it used in reviews I have to laugh.
About the time the DVDs were announced I noticed a lot of sites seemed to rush to cobble together reviews as Google was returning more hits for the movie than ever before. I think that's roughly when the first "borrowings" started.