OK I spent some time on subsite issues yesterday, but didn't finish.
The Oracle version seems to work though I've not committed my changes yet. You can create subsites and add members to them. There's no way for a user to join a subsite membership group themselves though. There's a "user-join" script but it's never called anywhere, and I've not tested it. In theory you could add a link to this script to the acs-subsite index page and enable the feature.
The PG version is failing because of what appears to be a broken port of a very complex view in the relations code. I'll be taking a look at this in the next few days.
Both versions of acs-subsite appear to have one serious scalabilty issue. The query that pulls up the list of users which an admin can add as members to a site looks like it will run very slow as the site grows. This needs to be investigated further. On the other hand, basic membership checks and the like should be fine.
