For acs-subsite, basically I put the entire web site under acs-subsite.
For example, for a simple web application, I'd put all the custom user interaction under my new subsite package and extend or override any subsite features to make them simpler or more specific for my application.
OR for a complex web site, I might have many subsites all with different descendant subsite types. In this case each sub-application has its own set of users etc so using a subsite makes sense. Again everything is put into the subsite derived package.
I generally don't use any existing application packages as they all contain too many assumptions or are just a huge set of switches which makes it very difficult to meet precise demanding user requirements. I just build all new data collection forms and displays and lists using the existing core features. It is kind of hard to explain in a forum post :) This mainly is due to the extremely unique requirements of my remaining OpenACS users.
