The change, he said, has to do with Google grouping more of the same category results together in the search results, thus pushing more diverse results to the second page. Tedster explains:
I think Google has been classifying types of sites for a while, and now it's getting more granular and sophisticated. This kind of sorting and classifying showed up a while back for some of the highly competitive searches. One day we woke up and WHAM!, the whole first page looked profoundly different, with very different types of sites (often informational rather than commercial) being featured. And the previously dominant domains were pushed down or off page one.
Robert Charlton also sums it up a bit more clearly with this one line:
I'm seeing page one dominated by results from one market, with the right column dominated by ads from another market.
Is this now being tested in some areas but without labeling them as categories? Is it possible Google is testing this for some search phrases, on some users, without labeling them? Sure, it is possible. I am not sure if this is the exact case, but it does remind me of it.
Forum discussion at WebmasterWorld.