A suggestion is to make a google search plugin, integrated with the ad sharing plugin.
Search forms is replaced by google search and ofcourse the results are displayed in wordpress (not a separate window). Advertising is displayed just like with ad sharing. If the user doesn't fill in their own ad-code the sites ads will display. If the user does put in his ad-code there is a split just like with ad sharing.
It could be a great complement to ad sharing and an other way to make some money out of your wpms site.