Nice, I just had the same thought and ended up in this thread.

this guy also had the same idea: http://www.physicsforums.com/showthread.php?t=516770

I think the effort would be quite excessive to enable this on a low level vm so programs in any language can run on it.
My motivation is getting decentralized application hosting in a manner tor does that for static web pages, with the possibility to be extended to scientific calculations and other number crunching.

The simplest solution might be to just use golang and it's abilities to run on distributed infrastructure.

Potential systems and OS for BTC mining network as single distributed supercomputing platform:

MOSIX VCL Cluster Platform - http://www.mosix.org/txt_vcl.html
"The VCL cluster platform allows OpenCL applications to transparently utilize many GPU devices in a cluster, as if all the devices are on the local computer."

Inferno - http://www.vitanuova.com/inferno/
"A compact operating system for building cross-platform distributed systems"

(update continuing...)

I don't think this can be incorporated into Bitcoin.  How would you implement proof-of-work?

This is very interesting topic.  I've been followed new posts to this thread since it was created because I got the same kind of idea.

I am a founder of cloud computing based Software as a Service (SaaS) -business. I am working with modern cloud computing software and I know it is not just a hype, especially when we can implement this kind of ideas to the market and share the profit.

I have discussed about this idea with engineer worked in Nokia Corporation and he thinks too this is possible to build. If it really is, I have a connections also to private investors and to development funding that my country public sector may offer - I am serious about that.

After when we know each other and we know that this technology can be build up, I think in the future some offshore company for example in Hong Kong could be the solution to incorporate.

I hope I can be contact with you soon about this great idea.

Found this project:

"OpenAdap.net is an Open Source project aimed at breaking the barriers existing in the flow of data access and data processing. The infrastructure will make possible the dissemination of resources like knowledge, tools or data, their exposure to evaluation in ways that might be unanticipated and hence support the emergence of communities of users around a specific domain. The architecture is designed by analogy with a virtual distributed operating system in which the dynamic resources are presented as files in a structured virtual file system featuring ownership and access permissions. " - [openAdap.net]

Since the last post's of this topic there has happened a lot in the cloud computing industry which I have followed. But there has been also good news for startup companies looking for funding - crowdfunding may a great thing for this kind of business ideas.

Currently I could have time to develop new business. I know developers really near to me who made this kind of idea to live in 48 hours. If you guys are still interested, let's discuss more about this idea and investigate could we find some possibility to develop this idea to real business.

P.S. This forum topic is still on the second page on Google search results when searching "p2p cloud computing".