pageoneresults - 3:00 pm on May 4, 2006 (gmt 0)

But don't they need to index the duplicate content to know it's duplicate content?

Not really. In this instance, I'm referring to query string duplicate content. As g1smd pointed out in another topic, vBulletin presents 12 different URI scenarios to the spider that all lead to the same content. Googlebot has been digging deeper and deeper into queries over the past 18 months. Personally I think it goes to deep into query strings and that's where part of the problem lies.