This topic came up in a month-old submission about why eBay lost many of its organic rankings in Google's Panda 4.0 release. Some of the comments from that discussion seem quite relevant to this one.

http://news.ycombinator.com/item?id=7788804

When Slate refers to eBay research, is it based on methods that allowed ads like this gem?

    Vomit sale
    New & used Vomit.
    Check out the deals now!
    www.ebay.com

(http://www.wordstream.com/images/panda-4-ebay-2.jpg)

If so, can we really take their findings seriously?