Some former colleagues, both old and more recent, have started a company called Ringside Networks, building a platform to integrate and host social networking technologies within corporate web sites. The company is releasing part of the source code on an open source model to drive adoption, so check them out: there's no cost and lots of transparency. I like the fact that new business models are emerging for startups, though the exit options are limited to acquisition, valuations have been high for companies with open source products that have gained scale.
In this case, the business model is doubly interesting, as it aims at a hybrid of SaaS and in-house technologies: part of the pitch is that social applications are too important to be captive to third-parties. If large companies (especially retailers) find that they want more ownership of their customers, this may be a very interesting play.