In the original WSJ article (yc: http://news.ycombinator.com/item?id=4741394), it's confirmed that this effect has a limited duration.

  > A Google spokesman said: "We aim to get users the best
  > answers as fast as possible" using techniques such as
  > examining "related searches." He said the goal for the
  > feature is to provide better results in a situation
  > where, for instance, a person who searches for "Harry
  > Potter," and then for "Amazon," actually wants "Harry
  > Potter" results from Amazon.com Inc. He said that the
  > technique saves Google users time and provides better
  > answers, but affects only about 0.3% of the searches the
  > company conducts.

That's not confirmation, that's a public relations response. Confirmation of limited duration would be actually running the experiment until the effect actually disappears.

    for instance, a person who searches for "Harry
    Potter," and then for "Amazon," actually wants "Harry
    Potter" results from Amazon.com Inc.

I wonder, is this really the case? It seems strange. Is there any research available about the frequency of such strange searches?