It's all anecdotal and so far I don't think anyone has actually found phones etc exporting conversation keywords or anything like that. That being said it's happened a few times that I've been in the car with my girlfriend talking about something, won't search anything about it and we'll get ads about it in the next couple days... The one time that stood out was talking about babies and getting ads about childcare, baby products, etc way more over the next couple days.