A simpler version of this would be to use fuzzy matching on the person's history of messages. Which would rule out copy-canned messages right away, and would also prevent them from just changing a dot here or there in the message.

I'm very interested in dating sites btw, and I have quite a few ideas up on http://ideashower.posterous.com (no time to go thru and pick out the dating-related ones right now, alas).

Edit: pulled them out via Google. Here they are:

http://ideashower.posterous.com/idea-misc-dating-site-ideas

http://ideashower.posterous.com/idea-dating-site-slideshow-a...

http://ideashower.posterous.com/idea-dating-profile-improvem...

http://ideashower.posterous.com/idea-dating-site-that-gets-r...

http://ideashower.posterous.com/idea-dating-site-with-gamifi...

http://ideashower.posterous.com/idea-walk-in-my-shoes-dating...

http://ideashower.posterous.com/idea-my-dating-profile-did-w...

http://ideashower.posterous.com/idea-dating-site-staff-of-fe...

http://ideashower.posterous.com/idea-smartphone-video-speed-...

http://ideashower.posterous.com/idea-adsense-for-dating

http://ideashower.posterous.com/idea-photo-album-widget-for-...