A few weeks ago I was working on a web site that wasn’t getting as much attention from Google as the site owner expected. One (of many) issues was that for every “interesting” page (those that had link-worthy material), there were at least three URLs for that same content. Depending on how the user navigated the site, they’d get to a different URL.
I pointed out that this is a Bad Thing, since distributing the incoming links across those duplicates would decrease the Google-worthiness of each… but hadn’t had time to write up the detals. Today I was thrilled to see this detailed writeup of the phenomenon and this one about how fix it. I’ve done the same thing in the past, but never written it up.
If your site has this “feature”, and you would prefer it gets more traffic, fix it.