4:18PM: Went to Google Maps and entered “Tirana” in the search box. This was a random act of curiosity: we recently had a conversation about Albania at work, and I was wondering how the city looks. I am certain I haven’t mentioned Tirana anywhere on the Internet within the last two or three months at the least, and perhaps longer. I was using Chrome and I was logged in to my GMail account.
5:22PM: Received an e-mail from hotels.com with the subject “Great Hotels in Tirana – Book Now!”
Conclusion: Most likely Google shares my map search history (and G-d knows what else) with third party sites, and it can be acted upon in a matter of minutes.