I suppose this is useful as a meta list of all the interesting things someone runs across as they're reading feeds, and you could get silly and subscribe to your own feed of shared items. But it's not usually that interesting to read someone else's feeds - unless that person is a celebrity or a friend.
Google may have picked up on this, and now Google Reader shares your feeds with anyone you have as a friend in Gmail Chat or Google Talk. Now this is useful. Instead of emailing your friends interesting articles you run across in Google Reader, you can just tag them as shared.