Legion brings your "contacts" out of your Address Book and places them, as people, in Gardens. Gardens are the focus point of Legion. In a Garden you can move people around and arrange them as it makes sense for you. People in Legion can have a customized look and you can assign keywords to them too, so you'll be able to tag people with their interests.
But the real magic of Legion comes from other people. Each user of Legion can publish a Profilecast that includes their interests, associates, and a little blurb saying what they're up to. Legion will automatically discover Profilecasts for people in your Address Book and their profile information will automatically be added to yours.
As Legion works away in the background, it uses this Profilecast information to determine if a person is interested in what you're reading. If you think it'll be of interest to them and want to share, just drag-and-drop the link or some selected text on them and a mail message will open up - pre-addressed and containing the text you want to send.