Personalized search is here and you shouldn’t be worried.  The search engines have been experimenting with personalizing the search results for each individual users for several years.  Google has been making the most public progress.  If you sign in for GMail or some of there other offerings, they will keep you logged in until you actively sign-out and track your usage and behavior.  Then they will start customizing your search results based on it. 

For example, if you are a plumber and you often search for plumbing supplies on Google, and then you search for seals, you should see mostly sites of seals for hoses and pipes and not sites about the new baby seal at the local zoo listed in the search results. 

Why am I not very worried?  Reason #1 - This technology is still being built and nothing is finalized.  So it is a bit early to be worried.  Reason #2 - In theory this will help drive more relevant users to your site.  If you sell rubber hoses and seals, you do not want kids looking for baby seals on your site.  Reason #3 - If you do get better targeted users with higher conversion rates, it could help you to increase the ad rates on your website. 

Don’t worry be happy.