There's a new Google hack (or something I was not aware of) in town, and I'm in love with it. It allows you to see an estimate of how many pages in a specific domain are supplemental results. To see the hack in action, just type the following at Google:

site:www.mydomain.ltd ***
i.e. SEOmoz, Skype, DMOZ

Most of the headlines are about how much "waste" google is storing about itself (site:www.google.com **) , but this hack is  very useful for checking competitors and clients.  Google, however, is far from the largest entity in supplemental results index. For example, Amazon has a whoping 15 - 64+ million pages (depending if you are checking with or without www.) in the supplemental index, and MySpace is in range of  5-71 million pages.