Here's a quote:
When we began work on Alfresco, our Open Source Enterprise Content Management System, we had two requirements. Firstly, to build a web-based client that would run as a portlet from within a JSR 168 Portal environment, and secondly run as a standard web application (see figure 1). Further, the application needed to be easily customizable and extendable by developers. JavaServer Faces appeared to be the natural choice due its event-based architecture, standardized component model and the promise of rich tool support. The majority of our development team had previously worked on defining the architecture for Documentum's Web Development Kit, which takes a very similar approach to JSF. In fact, some of the representatives of the team were members of the JSF expert group, so we knew we were taking the correct architectural approach.
Read Alfresco Chooses JSF for Enterprise Content Management System.