The biggest limiting factor in search right now is content quality. Google is pushing to bring books online. They not only want to bring millions of books online, but they also want to turn their pages into linkable web pages
What Google has not announced, but is likely to one day, are ways it might help publishers and authors enhance pages from printed books once they are online.
Cerf refers to this as "books that talk to each other," an idea to make them more like the rest of the Web where pages are cross-linked and visitors can annotate and tag text as is done with Web logs.
Olive Software is a company that stores print magazines and newspapers in XML searchable format, while making the content easy to read online in its near original format. Imagine if Google bought a company like that, and extended Google Base to include a large portion of the history of printed works.
If the linkage data was HEAVILY augmented by usage data and tracking what words people use in various forms of communication how hard would it be to have higher quality search results? If many of those books, chapters, and articles were easy to directly link at and either accessed via invisible tabs and/or direct integration into regular organic search results that flood of content would be able to drown out the profitability of many low quality content websites. Google already place Google Finance and Google Video in their search results.
What would happen to the ultra niche websites that have limited usage data, few quality links, and are of low social significance? Would the margins fall if billions of better than average quality articles were part of the search database? Would SpamSense even be profitable at that point if you created sites about topics you were not interested in?
Google wants to make it easy to consume, create, and share information. They make strategic partnerships with traditional media companies to offer free exposure in exchange for increased awareness of their new verticals. They are relying on amateurs to give them the leverage necessary to hopefully have traditional media companies opt into Google's way of thinking, and Google's system without having to cut Google's margins.
Google pushes hard to bias their algorithms toward true editorial citations and informational resources, forcing many spamming webmasters to ignore Google as a target. Yahoo! does not care as much about content quality because they have a boatload of it and want you to give your content to Yahoo!.
Yahoo! is pushing one way (all your contents are belong to us), and Google is pushing another (let's find a way to bring high quality content online). Both of those moves will hit margins pretty hard on thin margin junk content sites. MSN is also going to cut the value of many low value add business models, and in a couple years their search might be hard to spam too.
In 5 years will sites need a social aspect to them to be visible and profitable?