This is more about allowing people with lots of extra hard drive space a way to make money with that space, and giving people who need more space an opportunity to purchase it at a price that isn't insane.
Also, S3 is still high priced. $125/month for 1TB of storage. I'd be willing to provide 1TB of storage at a far lower price than that.
If it is not about backups, isn't the cost of it being offsite driving up the price needlessly?
Wouldn't your sister be better served by borrowing or renting a disk drive from you for her to use at her site, thus paying just for one sneakernet movement of the drive to her then someday maybe one sneakernet move of it back to you, instead of paying by the month for remote access to a drive at your site?
Or is this sister at the same site as you?
If you have reliable long term lack of need for storage, and she has reliable long term shortage, that seems a perfect setup for a used disks market even: sell her a spare disk and buy a better one later if some day you find you do afterall need more.
The closer you approach the fly by night laptops scenario the closer you get, it seems to me, to a situation where buying momentary storage instead of buying the media itself that the data is stored on starts to look reasonable. If you only need a few petabytes for a few minutes or hours, it might well make more sense to use it remotely rented by the minute or hour than to buy or rent a few petabyte drives for your own location.
So I think we need to figure that yes we are looking for fly by night laptops, however outre that might sound, and thus look for solutions targeted precisely at making distributed storage reliable even on aggregations of fly by night laptops.
Having to make rather extreme assumptions about the nodes being so utterly unreliable, to the point where we are not trying to insure our data against the occasional failure of a machine somewhere in our network but, rather, are trying to insure it against maybe even a 51% attack in which 51% or more of our nodes are with malicious aforethought carefully co-ordinating and tracking data looking for a moment in time at which all of them agreeing to refuse us service at the same time, deleting all copies of our files they have access to, can do us the most harm (for the lols, even, maybe) we can figure we want to ensure the default number of copies of any item of data should be far far higher on our proposed network than the maybe 3 copies to a dozen copies or so things like GNUnet and Tahoe-LAFS and so on typically figure people will configure their data to demand.
Our disk space is thus likely to make up in sheer volume required to keep many more copies of everything than a more reliable network would need a lot of any cost savings it might experience by imagining the space used is "essentially free due to being not in use" (when in fact just like mining, actually spinning up the drive instead of letting it hibernate might well drive up the electricity bill...)
There definitely are projects aiming toward the desired goals, except for the part about money.
Maybe anonymity might not be that great a feature once money is involved, since if Moriarty offers to store my data I might prefer to pay someone else more just to keep it out of his hands rather than pay him to store it for me? If I have to assume that the vast majority of the copies I am paying for of my data will deliberately vanish just at the very moment when I most need them, the price I will be willing to pay per copy maintained will be far far lower than if I am more confident that the vast majority of the copies will survive and be instantly available to me at high bandwidth from numerous sources...
Projects are working on all this, I have looked into those I could find, visited their Freenode IRC channels, given them a test drive and so on. From what I learned so far I have the impression that the main thing preventing GNUnet for bothering to have a currency yet is they are still tuning exactly what any such currency would actually buy, or maybe a better way of saying it would be, given some kind of currency, what exactly should a node consider how valuable compared to what else in order to intelligently decide what exactly to spend how much currency on.
That is, I got the impression that GNUnet was still in the process of working out what needs to be able to be compared in value in order to make purchasing decisions.
Thus I am still thinking that once GNUnet works well at actually trading the commodities it has at hand then would be the time to look at how best to set up mechanisms by which a node can be configured to give some nodes preferential treatment above and beyond that which is "deserved", so that bitcoins or whatever else could then be used to bribe any nodes of your choice into giving your node resources that your node has not "earned" by its own contributions. At that point markets could compare what bribes various nodes are willing to accept and nodes unwilling or unable to contribute their fair share of work/service would be able to shop around to choose who to bribe for what "unearned" resource-usage.
Bear in mind denial of service attacks, too. A market driven only by pennies might be quite vulnerable to anyone willing to throw dollars at it for a few hours to disrupt it. You might think there are a thousand laptops online at any given instant that have copies of your data safe and sound because each one of them each already learned you pay an entire satoshi per year per copy, but then suddenly one moment find every one of them threw away your data without notice due to hearing of an offer of a hundred million satoshis per decade per gigabyte per copy from someone else who might renege on their offer the very moment they realise their offer accomplished its goal of having everyone delete all copies of your data to make room for theirs...
-MarkM-