How to intercept new member registration

We want to automatically enroll new members in a Google Group. I can think of several ways to do this:
1. A plug-in, if CB triggers and event on new member registration
2. A cron job that scans the database for new members

What do you suggest for this? TIA.

Easiest approach would be CB Auto Actions and acting on the onAfterUserRegistration trigger. What action type you need I have no idea as am not familiar with Google Group API, but am guessing probably Code or if its an HTTP request then Request action type.