Today by popular request we're introducing email notifications for new Blog Posts and Forum posts in Ning 3.0. At the bottom of Blog and Forum listing pages (categories too!) you'll find a new option to "Follow" new items.
This will let you and your members stay on top of new content that's been added to the network. We appreciate your feedback on how important this feature is to your networks, and thanks to all NCs who have filled out the poll to help us prioritize the other features on our roadmap.