Danny Sullivan at Search Engine Land has particularly good coverage. An excerpt:
Beginning today, Google will now personalize the search results of anyone who uses its search engine, regardless of whether they've opted-in to a previously existing personalization feature.There now appears to be a big push at Google for individualized targeting and personalization in search, advertising, and news. Google now appears to be going full throttle on personalization, choosing it as the way forward to improve relevance and usefulness.
The short story is this. By watching what you click on in search results, Google can learn that you favor particular sites. For example, if you often search and click on links from Amazon that appear in Google's results, over time, Google learns that you really like Amazon. In reaction, it gives Amazon a ranking boost. That means you start seeing more Amazon listings, perhaps for searches where Amazon wasn't showing up before.
Searchers will have the ability to opt-out completely, and there are various protections designed to safeguard privacy. However, being opt-out rather than opt-in will likely raise some concerns.
With only one generic relevance rank, Google has been finding it is increasingly difficult to improve search quality because not everyone agrees on how relevant a particular page is to a particular search. At some point, to get further improvements, Google has to customize relevance to each person's definition of relevance. When you do that, you have personalized search.
For more on recent moves to personalize news and advertising at Google, please see my posts, "Google CEO on personalized news" and "Google AdWords now personalized".
Update: Two hours later, Danny Sullivan writes a second post, "Google's Personalized Results: The 'New Normal' That Deserves Extraordinary Attention", that also is well worth reading.