Yes please document this!
Regarding dotLRN it has its own group management.
In the future I'd like to look into revamping the core and standard subsite package to do stuff much like dotLRN does currently, with an eye towards merging as much as possible.
And another idea I want to explore is getting rid of the group membership altogether, leaving only relation segments around (which dotLRN uses heavily). Relsegs let you define subsets of groups, and there's no reason that "the subset that consists of all members of the group" needs to be special (relsegs were a late addition to ACS 4 and this may be why aD didn't take this approach in the first place).
IMO this might clean up the kernel some and I know for a fact that on a large installation like SloanSpace, with a couple of thousand groups and relsegs, that permission checking would speed up by a third.
Anyway ... if you'd document what you've learned I'd appreciate it.
And yes users should be added to the main site parties group automatically ... and if they register for a subsite they should be properly entered into the hierarchy, no?
