Can I offer a variation of this one? I care about privacy. I wouldn't want a human to be looking over my searches. That said, if they're just using the data to serve me relevant ads and it's all either automated or aggregated so that I'm never personally identified, then I'm cool with it at the personal level.
I say "at the personal level" because I think there's still a practical problem when it comes to politics. It seems too easy to sway elections using it. Not even necessarily by shaping the results in any way. Simply by being able to identify the groups of users who will vote a particular way in particular electoral divisions, and then seeking to lift their voting rate above the average. (eg. by prompting/reminding them to vote)