Can you force users to put all new content in at least one Organic Group? In Drupal 6, I would like to make sure users always add their Group content nodes to at least one Organic Group. I have a module that enforces a maximum number of groups, but I don't think it does a minimum.

The site is entirely groups-based and I don't really want people posting outside of a group.

I could certainly write a module for this if one does not exist, or it might be as simple as a form_alter() function.
In admin/og/og search the "Audience required" setting, and change it from optional to required, if you don't need it for administer accounts also.