Just commenting about Facebook ads, the rest is pretty accurate in my experience -
On FB, that's the remarketing side, and it's a lot more manual. Generally the goals and data will be selected by the advertiser themselves. It works, but it's a bit blunt-weapon-y - let's say it'll catch 10% of people who are absolutely going to convert, and 90% of people who are absolutely uninterested for campaign X. All percentages here are pulled from nowhere, they're just to give you a general idea.
Remarketing is popular because conversions. Also, if you're well-off or otherwise a desirable target, you cost more to reach through Facebook - so you're likely to see more remarketing campaigns, because automatic campaigns will adjust to target less expensive individuals until they've gone through all of them.
Facebook's automatic targeting is a lot more sophisticated, and much more in line with the suggestion engine idea. Let's say it will catch 0.2% of people who are absolutely going to convert, 9.8% of people who might possibly convert, 45% of people who vaguely appreciate the ad being there without converting (including people who might Like/Share/comment on the post), and 45% of people for whom the ad doesn't really connect. It's not usually quite as powerful for conversion, but on average it's pretty accurate at guessing if you'll be interested.
Also, StumbleUpon was a decent suggestion engine once upon a time - if they could actually design a proper extension that did something similar, I'm sure it would be a success.
On FB, that's the remarketing side, and it's a lot more manual. Generally the goals and data will be selected by the advertiser themselves. It works, but it's a bit blunt-weapon-y - let's say it'll catch 10% of people who are absolutely going to convert, and 90% of people who are absolutely uninterested for campaign X. All percentages here are pulled from nowhere, they're just to give you a general idea.
Remarketing is popular because conversions. Also, if you're well-off or otherwise a desirable target, you cost more to reach through Facebook - so you're likely to see more remarketing campaigns, because automatic campaigns will adjust to target less expensive individuals until they've gone through all of them.
Facebook's automatic targeting is a lot more sophisticated, and much more in line with the suggestion engine idea. Let's say it will catch 0.2% of people who are absolutely going to convert, 9.8% of people who might possibly convert, 45% of people who vaguely appreciate the ad being there without converting (including people who might Like/Share/comment on the post), and 45% of people for whom the ad doesn't really connect. It's not usually quite as powerful for conversion, but on average it's pretty accurate at guessing if you'll be interested.
Also, StumbleUpon was a decent suggestion engine once upon a time - if they could actually design a proper extension that did something similar, I'm sure it would be a success.