On your Facebook profile set your relationship status to "engaged" and you'll start getting a lot of wedding related adverts. Sure it's not the same as advertising when a user is searching Google for "diamond ring". But a lot of people will never search online for a diamond ring, but they may see an advert on their Facebook for a diamond ring and click on it.

Google strength is that advertising is based upon search intent, it's also their weakness.

Imagine you were De Beers and you wanted to target people on Google who were engaged but weren't googling for "diamond ring", you might think you could buy ads on related keywords like "wedding invites" - but it turns out Google make it very hard to do this. Unless your ad directly relates to the search term you get a major quality score penalty which means you have to pay a huge premium to advertise.

Daily deal sites have been spending a lot on display ads (on Facebook and elsewhere), precisely because of this, because their customers didn't actively search for "daily deal sites" so the only way to reach them is through display ads. And who has the most display ad page views in the world ? - Facebook.