Their entire business (advertising) is clustering. They've already done the hard bit. Just cluster people by downvotes and whatever other thousand metrics are

Their entire business (advertising) is clustering. They've already done the hard bit. Just cluster people by downvotes and whatever other thousand metrics are already being tracked, and allow them to see results given by other clusters by showing which areas are dense on a PCA or something or saying 'I want my results to only be influenced by people who have downvoted github.org' or whatever.