I (sirzooro) am not an author of this plugin, nor any other authors listed on this page (at this moment there are two more: GamerZ, ozh). Its true author is Adam Bell (agbell). He removed his name and placed our names instead - see change recorded in SVN. He is an author of another WP plugin - Random Pages Widget - For Visitors & SEO.
This plugin has following comment in its code:
This program is supported by ad space sharing. You agree to run its
developer's ads on occasionaly (5% or less of pageviews) on your site(s). By
using the program, you are agreeing to this condition, and confirming
that your sites abide by Google's policies and terms of service.
Interesting, isn't? Readme does not says a word about this. Moreover, parts of this plugin is encoded, so I could not confirm if it does ad space sharing only, or something else!