We know all about user-generated content, masses of users contributing to burgeoning Web corpus. It’s a manifestation of Web 2.0, the participatory Net, which companies like Google (YouTube), Yahoo (Flickr), Fox (MySpace), etc. are feasting on. In parallel, users are contributing a potentially far more lucrative Web currency–metadata about themselves. It’s the currency that will help Facebook grow into its $15 billion valuation. In addition, users are also contributing structured (meta) data about data, which will help the semantic Web to flower.