I've talked about what follows a number of times but only as disconnected bits; now I'm going to describe the forest rather than the trees. Some of what follows has already been implemented by a number of sites, some is in testing, some in research; however, it all is real and it all works if not as a whole live reality, not yet, quite.
Important Note: the following is simplified and limited, the reality is complex and far far more reaching.
You are warned.
A visitor arrives on site for the (apparent) first time and the default format for that landing page is served. Simultaneously the visitor is being fingerprinted (Visitor Identification, Cre8, December-2011; Mining Apps, Cre8, December-2014) and entered into a database.
As the visitor scrolls, moves mouse, etc. reading speed and interests, individual on page track and multiple page click tracks are logged, entered into DB, and associated with fingerprint id.
Visitor returns, is identified by 'fingerprint', prior site interests are checked against landing page content... and a personalised (rather than the default) format based on context of person, device, history, etc. Personalised Selling Is A Competitive Advantage, Cre8, December-2011.
Mine are pure info sites; what others with eCom sites are doing is taking personal ID from orders and mining SM for additional data to better pinpoint offers. This for your mother's birthday, that for your anniversary, your nephews high school grad... all apparently serendipitous but in reality your web shared personal information leveraged. With nary a cookie or registration on site.
I know which books or movies or media devices or what-have-you I sold you through affiliation and which ones you were checking out on my presell pages that you didn't. So, I can better target you each time you return. I know which ad pages for which products interested you the most over time so I know which coupons and offers to suggest first and second on given days in given seasons.
Back to the beginning: a visitor arrives on site for the (apparent) first time from a back link aka not via SE and that referrer is checked against a DB. If not there, the default format... (and is logged to be added)... however, if already there I already know the context of what brought the visitor: the referring page's title, heading, description, link's anchor/surrounding text and subheading... and a semi-custom context driven page format and content is delivered and visitor is fingerprinted for future reference.
Yes, there is a fly (possibly - still too early to say definitively) in the ointment for those that live and die via Google: not every visitor sees the same page at a given URL; there is a default and then there are the personalised. It is using context to change content - remember how innovative was CSS? - this is a similar shift. The page is becoming a recombination of URIs under an overarching URL.
In time (still in research stage) a site may become a recombination of URIs packaged according to personalised requirements. rather than move from formal page to page one would move through information chunks (I don't have the computer power to go more granular in real time).
The web is still wild and increasingly weird and loads of fun...
And the revenue rivers overflow with goodness and money.