Earlier quoted context omitted.
"groups of content" are collections of content that users create themselves (the social bookmarking aspect of the site). Users that want to build a reputation for being in the know and influential are incentivized to make these collections relevant. The groups also become lists users can form to bookmark content they find around the web and want to save it one spot. Based on what you have put into your collection of…
In other words, I make a "group of content" that I call "movies" and it gets compared with other peoples' "group of content" that they called "movies". Why isn't the netflix recommendation system useful for generating recommendations from "groups of content" labelled "movies"? If it works for movies, why can't it combine "groups of content" labelled "science fiction"?
For example I can make a group of content called "new living room" and add all of the things that go into my new living room. This includes the music and movies that I have stored there, the type of TV I bought, the type of couch, stereo receiver, speakers, or even the paint on the wall. When someone searches for something within that collection, the system knows that someone else, somewhere, has combined that "thing" with the other "things" in the collection, so they get rated higher as being compatible.