If anyone is going to work on this, please let me help. I have decided to use the subsite feature and I already had to change the datamodel.
Ben of OpenForce suggested that his folks had solved some problems they found, but he didn't elaborate. One I found annoying is that when you login/register you see the main site info.
One thing definitely needed is the ability to place users into a specific subsite group. The ability to create subsite types is also a great organizing idea. This needs to have a tcl or pl api so other packages can create new subsite types easily.