You can use it to:
- Engage coworkers, friends, and family
- Connect to other departments within your organization and globally
- Post projects and project team members so the entire company is kept informed
- Allow individual blogging, discussions, groups
- Share videos, photos, and messaging
- Socially-engage - interact with others that have similar interests
Ning also offers some premium services such as domain name, remove Ning promotional links, remove ads or control the ads that appear on your site, and space and bandwidth upgrades for a small fee.
This is a great service, and if you're looking to start your own Social Network I really recommend you look into Ning.