number cruncher

Nike has discovered that there's a magic number for a Nike+ user: five. If someone uploads only a couple of runs to the site, they might just be trying it out. But once they hit five runs, they're massively more likely to keep running and uploading data. At five runs, they've gotten hooked on what their data tells them about themselves.

- The Nike Experiment: How the Shoe Giant Unleashed the Power of Personal Metrics