John Udell wrote recently about how Google is indexing his site in weird weird ways and how a lot of the trouble started because his web-pages are served with auxiliary content along the sides. That content may be completely irrelevant to the main topic of the page but google will index on it anyways. He suggests one of the big three search engines might figure this out but I think there is something that can be done on the edge in the interim.

It would presume that the website employed some templating engine or was largely stylesheet driven. If it were then I don't imagine it would be too difficult to modify the template or stylesheet engines to use a different template or stylesheet when the referer matches a well known search engine's robot.