I thought that most of what is searched is users home pages and other such dross. If a web index/crawler only indexed commercial stuff then it might draw more advertising revenue.
Or how about this. Indexes with a theme, indexes of say travelling might draw renvenue from holiday companies. etc. etc.
Client side :- Java applet using public key encryption to order goods using VISA etc. found in the database.
Single player games are also difficult because the state of the game has to be kept. Therefore if two hundred people are playing a game of one server the info has to be kept somewhere and managed.