I haven't seen this possibility noted, but perhaps Google has included actual feedback recorded through the use of its toolbar into its search positioning. Both the raw volume of site vistors, hits on that site, keywords used to find the page or site and perhaps duration. These stats might have been recorded over some months and only now used. New sites might artificially (but automatically) get boosted to see what results they get, then either retain their position or sink.
That would most likely result in sites with high traffic being given a boost, thus boosting generic listing sites and bigger sites. In particular we would see this effect if only the domain name rather than the full path was recorded by Google (from the toolbar).
Equally, sites with very high traffic for one or a range of terms would then position well for terms that had little relevance but were actually on the site even if poorly optimised.
The results that I am seeing on my site stats and the position of key words that I have 'tried' to optimise for on different sites seems to indicate the above.
This being the case, I expect that the churn on the google results will be high over the next few weeks and months, the implied feedback with users not accessing high listed portal sites but looking at pages 2 and 3 or more of the google search listing then working against the portal sites with the result that they fall off the listings for those terms?
The long term impact? If the above is so and Google's algorithm that includes this information works, then I believe we might be on the verge of an even better Google with position based not just on
SEO but also site quality - people stay on the site longer and that fact is recorded. There will still be work for us, but we will have to ensure that our customer - the person who asks and pays for the site to be created - provides high quality and useful content along with an agreement to buy in to ongoing development.