A Ponzi scheme is where new investors pay returns to existing investors, but there is no actual trade made using the income.

EDIT: Oops. Explained adsense. Too much multi-tasking. Irrelevant anyway, since PageRank does not have any of the above characteristics.

Per prior comments, everything is not suddenly a Ponzi scheme.

PageRank is a tool used to rank web pages in search results. But maybe Google is a Ponzi scheme. Users create all the content, Google sells all the ads!

<Brain Explodes>

Not everything is a dang Ponzi Scheme! Sheesh.