Earlier quoted context omitted.
Google, whose core business model fundamentally depends on extensive data-mining of user information? Does it? Try Googling from an incognito window on your neighbour's wifi. Use a live distro if you want to be completely sure. Are the results significantly different? Are ads any worse? I have tried a couple of tests like that (on other people's devices, etc) and the only noticeable use of that trove of data Google h…
Have a look: https://www.google.com/settings/u/0/ads If you don't trust that, then a great way to find out what any advertising company knows about you is to act like an advertiser and look at what user data you can get. I don't mean call up google advertising and pretending that you're head of marketing at $BIGCOMPANY (you could, but it's not what I meant), but try looking at the product pages made for advertisers.
But of course in order to do that, you also have to have a login, cookie, etc. for a panel that Google controls, and that exposes only a tiny subset of the information it could most obviously and trivially correlate about user activities.
These just aren't really things people trying to visit wordpress sites should have to consider..