We built a system for one of our clients, College District, that allows them to launch e-commerce sites fairly easily using a shared framework, database and adminstration panel. The first of the sites, Tiger District, launched over a year ago and has been succesful in selling LSU branded merchandise. A few weeks ago the following sites were launched on the system: Sooner District, Longhorn District, Gator District and Roll Tide District.
The interesting parts of the system include a single Interchange installation, serving two catalogs, one for the administration area and one for all of the stores. Each site gets it's own htdocs area for it's images and css files (which are generated by the site generator using the selected colors). A cool part about this setup is that a new feature added appears on all sites instantly. The site code uses the request domain name to determine which user to connect to the database as. The heavy lifting of the multi-site capbilities is handled by a single Postgres database which utilizes roles, schemas and search paths to show or hide data based on the user that connected to the database. This works really well when it comes time to makes changes to an underlying table, instead of having to update the same table in 10 different databases, the change is applied to a single table and all sites are effected by the change.
Additional sites will be launched in the near future as well as some great community features soon.