The current toast of the web is Pinterest, the visual pinboard for collecting and sharing content online. The “pinning” phenomena is spreading from its modest beginnings to appearing in national media outlets. There are over 2.5m monthly active Pinterest users on Facebook. A co-founder of the site has over 500,000 followers on Pinterest. Ron Conway (an investor in the site) remarked that Pinterest’s user growth rate is what Facebook’s was five years ago. Earlier in 2011, it was valued through venture financing at $40m and, most recently, just a few months later, at around $200m.

What is going on here?