Many open source software projects have started to experiment with Facebook to facilitate social networking within their community. Alfresco has taken things to another level by building an integration with Facebook to surface the Alfresco repository in a Facebook application. I think this ties nicely with the concept of using Facebook for the social networking aspect of your Intranet.
Of course, this strategy has its liabilities. The integration requires development work and the result doesn't always function smoothly (try searching for something on the Alfresco and you will see what I mean). Some customers just want everything out of the box (even if the features are lame and never get used) and don't want to be bothered with best of breed if it requires expensive and risky integration. However, I think it is safe to say that most current Alfresco customers (who were attracted to the product because of its architecture and standards support) like the idea of integration and service based architectures.