It sort of bugs me that whatever I search with Google haunts me everywhere I go with ads. They spy on us and then try to sell it back to us. That has stopped since I switched to DuckDuckGo.com, which does exactly the same as Google, but doesn't spy on us.
There's a fascinating podcast about cyber-tracking and how they profile you on fivethirtyeight:
Internet Tracking Has Moved Beyond Cookies
They suggest using "Ghostery" which helps to limit the tracking