So, what if you take the principles behind BitTorrent (share more bandwidth to get more data) and put them as a way to store your own, personal data? You get something interesting.
Allmydata attempts to do just that - building a storage grid that can store your data, without a centralized storage server. For every 10 MB you offer on your harddisk, you get 1 MB free for your stuff on the Allmydata grid. Which means that your 1 MB is going to be replicated on 9 other machines on the internet (of course in encrypted form).
The advantage is that you do not need to worry about backups anymore. Or, at least in theory... :-)