My worst imagination is labelling you and selling your label to the companies they supply to, and how wrongly those companies can use that data, example: google search “prostate cancer” or searching for symptons associated with prostate cancer - label telling probable prostate cancer developing with this user - insurance companies denying insurance to you or making it too expensive. Now extrapolate this to what your searches probably tell about you or your state, and multiply by the websites you visit, the time you spend reading article/tweet/forum/post about a certain subject, where and how you comment those articles, etc, and being labeled according to their perceived likes/hates/problems about yourself.
bananaghost