## post model

after_commit :share_all

def share_all
  user.share_content title, content
end

## user model

def share_content title, content
  # whatever stuff you have to determine whether it's a twitter and/or facebook update...

  if go_for_twitter
    twitter.update title
  end

  if go_for_facebook
    facebook.feed! :message => title
    # ...etc.
  end
end