In our ongoing September SERP Changes [webmasterworld.com] thread, gehrlekrona made an observation that I feel is worth some extra attention.
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.
Search terms themselves can also be sorted into various taxonomies, especially the 1-word and 2-word queries. Search term taxonomies could be built through "user intention" studies, which are especially challenging for those short queries. Many members here have mention the recent earthquake we;ve seen in the result for many 1-word searches.
With the advent of Universal Search, Google now has the infrastructure to force integrate selections from any class of websites onto the first page. So the implications of Universal Search can go well past the obvious and publicised taxonomies of images, video, news, books, maps, blogs. Even more than a simple "commercial" and "informational" taxonomy, there could also be classes like brochureware sites, trademark holders, businesses with a physical world presence, manufacturers, B2B, multi-topic (encyclopedic) and on and on. One factor Google could then tweak would be which classes of sites to force integrate into the results for which kinds of search terms.
This forced crazy-quilting of Page 1 might well push more users go to Page 2 - and that may even be seen as a potentially positive evolution at Google. It does give more ad impressions, for instance. I'm not saying this is the only motivation, not by a long shot. But it would be one kind of positive outcome as long as there is no negative impact on market share. And the average search user might well appreciate the variety of choices. Time will tell.