The startup I work for, Bizo, has had some clients doing similar things with our API:

http://developer.bizo.com/documentation/bizaudience-api

E.g. customizing their home/landing pages based on the business demographics of users (is this a small business user, Fortune 500 user, etc.).

(Don't mean this as a gratuitous plug, it's just cool to see the same client-specific customization technique used elsewhere.)