If you edit your account settings, you will find some new options for Organic Group email notifications.
You can disable it entirely, enable it for all groups you are subscribed to, or selectively enable it for each Group.
This gives you the option of receiving an email as soon as anything new is posted - whether it is a new forum post, a new page, a new blog entry, etc.
Also be sure to click on the 'Browse Groups' link (More Navigation, left hand column) to review the Groups on the Hive. There might be new ones that you want to subscribe to! We'll try to be more careful in the future to let everyone know when a new Group is added.