Here's an interesting site that compares "twin" ads. It's interesting to see how frequently seemingly copied ads win awards while the originals do not.
It reminds me of a Bruce Bildsten quote from Cutting Edge Advertising:
"The more I judge shows, the more I realize that people do come up with similar ideas. That's why the presentation of an idea can make such a difference. Because people are thinking in similar ways, it's more and more incumbent on you to execute everything to the finest detail."
