I saw a talk by the author of String::Trigram, and he mentioned that he used his module for a similar problem, determining whether a webpage had changed or not. If you tune your similarity threshold good enough, this could be another measure for "page similarity" respectively "These two urls are the same page".

perl -MHTTP::Daemon -MHTTP::Response -MLWP::Simple -e ' ;    # The  
$d = new HTTP::Daemon and fork and getprint $d->url and exit;#spider
($c = $d->accept())->get_request(); $c->send_response( new   #in the
HTTP::Response(200,$_,$_,qq(Just another Perl hacker\n))); ' #  web
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