Here is an interesting idea of combining the power of several computers (in this case PDA's) to perform a particular task.
Spb Software company has created a cluster of twelve PDAs that distributes the task among the nodes using infrared connection.
http://www.spbsoftwarehouse.com/about/pressreleases/2003/pocketcluster.htmWhile they do not claim that it is a practical solution, there is something about the idea of extending, distributing, and utilizing all available resources.
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P.S. I remember reading about a chess contest where Players were allowed to use computers to make their decisions. The guys who won the competition – were not the chess champions, and they did not own a supercomputer – they just utilized several of their home computers by running them agains and parrel to each other using different chess programs.