Martin Kearn who is one of the guru Microsoft Consulting Services in the UK team has written a really great blog post on the business data catalogue which he reckons is the best feature of SharePoint 2007. He also presented it to our special interest chapter today.
The BDC makes it straightforward to link SharePoint 2007 to other data sources. All the work that you used to need to do with web parts to link to back end data sources is made a lot easier. SharePoint manages the connection and the metadata needed to understand the back end data. BDC webparts then make it very easy to add these to your site.
I'll see if I can persuade him to record a demo blogcast as I think this would be very interesting to people.