They do in a way: they sell ads based on how well they can target the advertiser's desired audience. So they'll tell the ad customer all the categories that are possible. Apple, especially, has some detailed information because of iTunes. I've read... but don't take as fact... that one advertiser was told iAds could target age, sex, income, app and music purchasing tastes, and even sexual orientation (apparently inferred by the music downloads). Partly. As you know, Google lets you edit our core ad profile. I think, like you, there was some topic I had done a lot of searching about, but it was no longer an interest, so I removed it to prevent ads about it. I think it was car buying or something. I'm mostly okay with it... because it is handy when doing searches... as long as they don't share my personal info with the government. The not-mostly-okay part is this: it's pretty easy for someone to come to your computer and start doing searches and find out the areas you've been searching, simply because previous personal searches can pop up unless you've taken care to delete them. Absolutely. Which is why, on the other hand, we need (and have some) government laws to keep that info private.