David Cotter: the current model doesn't support what you envision. though perhaps we should make it do so. Currently, when you register you're always added as a "registered user", which is synonymous with being a member of the "main subsite membership group". You have to be added to a given subsite later.
Dave Bauer: sure, let's see those improvements and try to fold them into 5.0. Since you've not bugged me about groups and relsegs lately I assume you got everything working correctly for your project?