The search algorithm that Google uses is heavily weighted toward sites that are popular, to those on a particular topic that are visited more often than others and have garnered more links than others. That's basically the idea behind pagerank which was Google's original claim to fame. I have no doubt that this was a wonderful concept, and it surely generated better results than simply identifying the desired search term in the first paragraph of a page. But pagerank assumes that a particular result that has relevance to my needs has relevance to someone else's needs as well, and as flattering as that thought may be, I find it hard to accept. If our searches were primarily product oriented - toward finding the best digital camera, or the most successful recipe for chocolate chip cookies - a concept such as pagerank might be very useful. But that's hardly the case when what we want is interesting and thought provoking information on a topic we're trying to examine. I make the perhaps dubious assumption that when people are searching for information on the web their needs are specific enough so that the most popular site - the one most visited, or most linked to - is far from necessarily the site that actually has the information that they actually want to find. That being the case, I doubt that the information on my search habits that Google is able to collect, vast as it may be, helps them much when it comes to fine-tuning their algorithm, and since only a very small percentage of my searches are oriented toward purchasing something, serving me ads that are connected to my searches has only minimal influence over me.