> Ads certainly don't feel like much of the FB experience, nowhere near the level of Google, or even Twitter.

Facebook creates an artificial distinction between labeled ads (which are, of course, obvious ads) and posts with paid reach (which are also ads, but presented as normal content), exactly for the purpose of maximizing the quantity of ads while minimizing the impression of content being dominated by ads.

Not necessarily Ads in the traditional sense, but FB also sells content reach (Promoted Content) and targeting

Shaping the feed is certainly one part of it. But I guess that part of the success of FB is that they don't make it, as you said, not make the ads feel as much part of the experience.

Categorization is critical to boosting precision in information retrieval tasks. Deep networks for cropped object recognition are an important source of (inferred) content categories (especially when other context, e.g. photo captions, are not useful). While a good image categorizer would be very useful for ad targeting and auctions, the technology can also boost precision for news feed, graph search, etc., which improves user experience.

Agreed. You can't show ads unless you have users. Optimizing advertisements is definitely second fiddle to optimizing the user experience.

Someone with more context can answer this better but I would guess that selling behavioral data to ad agencies is a thing?