This is just me throwing out a toy idea here, but.. Consider that most computers have large chunks of unused space. Now draw a parallel to projects like Folding@Home which make use of unused CPU cycles for computation. Wouldn't it be nice to make use of the world's unused storage in exchange for providing your unused storage? This made me think of that as it sounds like this 'p2p supercloud' could be just another peer type. You opt in to share 100GB == you get 80GB of redundant off-site backup for free type system.
Now, I am not asking you to implement this peer type (although that would rock my world if you did), but would it be possible for someone to implement it themselves? In other words will you be providing a 'peer API'?
80GB of redundant storage = 160GB at least. More than that, because you can't count on any one node almost at all, so you need more than two copies.
This means you should get more like 10-20GB per 100GB you commit, otherwise the cloud simply will not have enough space.
Then if you consider that even with many nodes containing your data, there is a decent chance all of them go offline at a certain time. You have to have many, many nodes for the odds to be small enough. Which means the best solution is to use the storage you committed as one of the nodes, so it is always available to you. Then, it really transforms into a cloud backup system, rather than a cloud file system.
I've used wuala for linux and have found it quite rough around the edges.
* not completely decentralized or open source. If wuala goes out of business, your data may not be recoverable.
* web interface is lacking (poor folder navigation/listing)
* doesn't work without X on linux
* even with X, not all features are available through the command line or API, though some are
* the interface that is provided is clunky
* the status messages leave me wondering where in the process an update is. If a piece of software can't reliably tell me where it is in a process, I can't trust that the process is happening the way I expect.
Yep, Wuala is not completely open source and it is a business. Your worry that they might go out of business soon is mitigated quite a bit by the fact that they have been acquired by LaCie  over a year ago.
I suppose Linux definitely isn't their main market and while the Web Interface is lacking at the moment they are working on an overhaul.