Make It Rain
If virtual pennies (actually, one Bitcoin is worth nearly $20 because of recent press interest) can motivate users to buy more hardware and share their computational power for an arbitrary computational job, imagine what such an approach could do for clouds. Amazon has a program (Mechanical Turk) for “crowdsourcing” human-interactive tasks (e.g., writing captions) with rewards.
A reward-based system with a decentralized network would be more resilient than many cloud providers, as work could continue as long as internet backbones stay afloat. Since the cloud would be made of unsecured systems, it would be necessary to make the work inherently secure.
This could be done by applying some reversible transformation to the data before it is sent to the cloud for computation or by splitting the work so that a large fraction of the systems would have to be monitored to discover the nature of the work.
Redundancy and robustness would also be important, as individual systems drop in and drop out of the distributed network and suffer problems.
Such considerations in designing software and handling sensitive data, though, would be a wise investment regardless of whether the software would be running on Amazon's servers or gaming rigs. Whether it's due to an operations engineer or a smooth operator, or maybe an electrical storm, you don't want to get stuck because of a tangled network.