We're using Microsoft Sharepoint for our MDC back-end. This already has great out-of-the-box functionality. The team went to the latest conference in October and were delighted to see that SharePoint 2010 has a built in taxonomy engine. Ontologies here we come.
 
 
After the great meeting with David Flanders, we're now implementing our disproportionate feedback to the user. When the user makes a deposit in the repository, instead of a simple 'OK' message, we return a cascade of extra information that they might be interested in. Simliar to the Amazon's "Customer who bought this item also bought" feature. We return other datasets that are related to the one deposited. Hopefully this will delight the user  and make them come back for more ;)