Creating a Custom SharePoint 2007 Portal Site Definition using the PortalProvisioningProvider Class

Creating a set of sites and subsites for multiple teams by creating each site one at a time can be a bit of a drag and a definite administrative drain.  What would be nice is to be able to specify a set of sites in a predefined heirarchy that the can be used as a single reusable template.  This set of sites is what SharePoint 2007 calls a "portal" (The most overused word in the SharePoint world).  SharePoint 2007 gives you the ability to create a portal site definition by using the PortalProvisioningProvider contained in the Microsoft.SharePoint.Publishing assembly.  This class parses an XML file and builds the site heirarchy defined in the file.  Creating a set of sites and subsites for multip