Have you seen Windows Live Quick Apps? These are downloadable, fully featured applications that you can use to build social networking sites for a variety of out-of-the-box applications.
There are four applications, all of which you can download from CodePlex:
- Contoso Bicycle Club (demo)
- ContosoISV (Customer Relationship Management) (demo)
- AdventureWorks Resorts (Hospitality) (demo)
- Contoso University (demo)
These are pretty slick and quick, and can save you a lot of time getting your portal site up and running!