You've been
profile ranked
The only ways to avoid this are not telling them and not letting them find out your particular search habits.
That is, no toolbar, google account, surf with rotating proxies, block adsense/javascript etc etc..in other words jump thru' a lot of hoops.
What you should do for SEO is turn the tables on them and create thousands of fake users who tend to like your sites a lot.
Then when they start to profile rank a new "real" person who is searching for niches you target, they will begin to show him/her your sites as in the "people who like triple-anal-midgets.com also like little-people-large-genitalia.com"
Therefore the surfer will visit your sites more and more as they will be displayed more and more and he will umm buy stuff.
