One of the core reasons for developing this solution is that sites do not have the ability to directly store metadata about themselves like documents or list items do, at least not a place that can be populate without code.
The SPSite and SPWeb classes do have various properties like Title, Description etc which is what we use to populate the default fields in the site listings list, however the only way to extend these properties is to use the SPWeb.Properties
collection which you can only add and access via code:
My recomended approach here is to use the site listings list as the only place where you store site metadata, add your collumns here and perhaps look at extending the Site Data Webpart so that users can directly edit these fields from the site
itself...... this is something we are considering for a future version anyway (right now it simply gives a link to eth site listings list).
I hope that helps ..... please rpely here stating what you final approach is and if there are any extensions to the solution that we should consider which would make it better in this area.