<A target="_blank" href="http://www.newscientist.com/article/dn18721-data-sifted-from-facebook-wiped-after-legal-threats.html">Many researchers have employed "crawlers" to extract public information from Facebook</A> and other sites. Some have gotten permission in advance, some haven't. But, so far, only Pete Warden has been threatened with a lawsuit if he didn't delete the data he had collected.