I posted the following announcement on the SF Fandom Forums' General Discussion forum. I don't have the time and energy to rewrite it.

Yesterday, Friday, December 5, 2009 Google announced that all users of its service will now be automatically opted in to its Personalized Search feature.

Personalized Search, previously available only to people who were logged in, tracks your queries and clicks on search results. As you click on Web sites repeatedly over time they will move up toward the top of your queries. You will no longer see "natural" search results if you click on the same sites many times.

Although this is often a helpful feature, it does make it difficult for users to find new content they have not previously clicked on.

You can opt out of feature by clicking on "Web History" in the upper right-hand corner of your Google page. You must PAUSE Web History (in the lower left-hand margin) and CLEAR RESULTS to remove your Web history.

Google promises to remove your Web history after 180 days (but that means they will maintain a constantly scrolling 180-day window).

Google is using a "secret cookie" to maintain this functionality for people who are not logged in. It is not tied to the Google.com domain.

If you do not want Google to track your search history, you MUST opt out of the Web History/Personalized Search feature even though you are not logged in.

Search Engine Land has a lengthy article explaining what Google has done and showing you with screen captures how to disable your Web History.