I came across a strange occurrence of my site showing a weird parameterized version of its homepage when doing a site: command on Bing and Blekko.
Keep in mind this site is PR8 with plenty of links going directly to the normal page. This parameterized URL looks likes a PPC URL. It's got 4 links from SERP scraper sites (meaning its been in the SERPs for a little while, at least).
It doesn't show on Google at all.