To an extent its already going on. Google already offers the ability to tailor search results (and therefore ads) based on your browsing histrory and profile .Well for the advertiser tis is good right? Surely if your ads are placed in front of more targeted more qualified search engine users you can reap better results. Maybe, yes, but its also (if not optional) likely to annoy the hell out of potential customers. One of ther great features of the internet that makes it possible the greatest invention ever is the liberation of knowledge (anything is at your fingertips) and the anonymity of the search experience. You want to research your next car purchase but cant face the dealer sales bullshit, fine find  a million reviews for free abotu the very car you are interested in. Identify the 0-60, mpg, impartial lowdon on its reliability, resale value etc etc. Of course this is one example and being frank there a million more uses 'we' use the internet for e.g. its the biggest porn channel in the world - do you really want those search engines knowing your browsing history???

The founder of the web himself, Sir Tim Berners Lee  (note: ironically he has an awful website!) says himself that such privacy intrusions are unethical.  

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