In addition to that, searches automatically are tailored based on what a user is looking for in a particular country, and has been doing so forr years.
The difference now is that Google is tweaking results based on the individual user's behavior. Horling says many of these changes are rather subtle. "When these techniques fire, the changes tend to relatively minor," he says. "We're moving a few results. We might be moving a few down. We're generally not changing the entire character of the page."
In early December of 2009, Google also began personalizing based on the cookies stored on any particular machine.
Google is also tailoring results to the user's particular metropolitan area or local region. Basically, the idea is provider greater granularity of results, based on as many behavioral and locational clues as possible.
Apparently, Google also is using contact information mined from Gmail and Google Chat or Buzz in its search results.
There are likely some implications for search optimization, as each user, in each place, on discrete machines, with discrete social networks, will see slightly different results when using the exact same search term.
That probably will defeat some amount of search optimization. That might not be such a bad thing for users, though some optimizers will not like it.
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