According to Wikipedia, Facebook is a social networking service that is used by 85% of all college students in the United States. It is the 7th largest site in the US and even tops flickr in terms of photo uploads. Rolling Stone even calls Facebook the hottest site on the web.
More interestingly though, the technical details clearly endorses RIFE as being an excellent framework. They even include the custom authentication system that was written to integrate RIFE's authentication system with the facebook development platform and log users in with their regular facebook credentials.
This is a wonderful public acknowledgment of the uprise of Uwyn flagship project, RIFE as one of today's Java frameworks of choice.