Peter,
Roberto is right in saying that it doesn't relate to adserver in any way. Classified ads have provisions for extensibility via custom fields so it's aim is to be generic as possible. This means that you can use it to accomodate real world scenarios where there are categorized products. I used it for an apartment rental site where the ads are the available rooms, Paul Doerwald used it for a Jobs Posting package and I think Roberto aims to use it for a hierarchical catalog of books. Notice that each have their own unique properties but also share a common trait -- they being products that can be categorized.
