Recently some of my friends mentioned that they got invites from me in two of these social networking sites. It sounded strange since I never sent invites to those people. Now my fears have come true. Both these sites are misusing information that one provides to these sites. See following links.
http://www.librarything.com/thingology/2007/11/shelfari-spam-basically-social.php
http://www.observer.com/2007/caught-shelfari-s-sticky-web-no-more-friends-please