Users sign up for an account from FriendFeed, add in the services they'd like to share then friends can create an account and subscribe to their feed. It's that easy! You can see when they upload pictures to Flickr, add a new book to LibraryThing, bookmark a new site on del.icio.us, start listening to a new station on Pandora or Lastfm and 30 other sites.
Check out MRRL's feed patrons who want to keep up with MRRL's happenings can do so in one place. You can even have the Feed digest sent to your email each day.
This can be a great time management tool. You can even great Imaginary Friends to follow the feeds of friends who haven't signed up for FriendFeed.
Like many sites there are some great privacy settings, your feed doesn't have to be public.
If you're interested My Feed.