A funny feeling when certain ideas swirl through meme space and similar thoughts occur to physically very distant people. This occured to me when I read a column on PBS from Cringely (link). He talks about creating a distributed network of nodes to backup data to. One of the basic principles he states should be that users could backup only as much they provide to the system at large.
Couldn't agree more, I came to that exact conclusion myself a couple of months ago. I was thinking of a general purpose storage system at first. However, an associate of mine pointed out that it would be great to have an easy to use backup software and boom I came to the same idea as Mr. Cringely.
The challenge might be of a technical nature at first. Once the technology is in place though I see that the issue will more be one of 1) building a software that will be ultimately easy to use and 2) finding a working business model if ever you want to make money with this.