Index: helpers/application_helper.rb
===================================================================
--- helpers/application_helper.rb	(revision 18580)
+++ helpers/application_helper.rb	(working copy)
@@ -1,6 +1,6 @@
 module ApplicationHelper
   def htmlize(text)
-    return sanitize(auto_link(simple_format(text), :urls))
+    return sanitize(auto_link(simple_format(text), :link => :urls, :href_options => { :rel => 'nofollow' }))
   end
 
   def html_escape_unicode(text)