This is where Netflix ratings really shine. The Big Lebowski on my Netflix profile shows as five red stars. On my wife's, it's two red stars. Netflix guesses that I would really like the movie, while they don't think my wife would enjoy it much at all. And that's completely true. However, they give her a rating of five red stars for Masterchef, a show she actually loves. They give me four red stars, because I've rated other reality shows and other cooking shows lower in the past.

So if Yelp had that kind of thing, this person rated McDonald's highly, they'll probably like Burger King. This person liked Subway but hated McDonalds, so they'll probably like Jimmy John's but not Wendy's. Even more specifically, this person liked Wendy's spicy chicken sandwich, they'll probably like Subway's sriracha buffalo chicken sub.

That's the kind of investment and innovation that drivers user interaction.