Lauren Weinstein writes how one might disperse pieces of a message along with an obscure search key throughout many unrelated comments. Searching for the search key aids one in finding the pieces.

blog: http://lauren.vortex.com/archive/000476.html

example: http://lauren.vortex.com/searchwiki-secret

Wasn't this always possible with any website?

Just search for "the monkey flies through the hula hoop" in a minute ;)

The message is: You are the red monkey!

I don't get it? How do I find your hidden message throughout the pages and pages I get as results for "the monkey flies through the hula hoop"

I guess the idea is to hide the messages so that nobody can see them if he does not know the search key. If the messages are hidden on webpages, they could be discovered by some "intelligence crawling". Search comments are hidden in this way.
But i am not sure if this is really useful as Google can change the order and/or items of the search results so no one can guarantee they will be there...