Assuming it goes open-source (or at least the protocols do, so it is properly reviewed), this is a great idea as you get all of the benefits of "the cloud" without having to open your privates to those you don't trust that much. Like MS, Google, Amazon, etc...
Ideal for extended families so a selection of machines can share files and act as back-up for each other.
Of course, if it has a "read-only mode" (i.e. original creator can make changes that propagate across all shares, no one else can) then it could stir up a lot of controversy as The Pirate Bay's web site could become a local searchable share on thousands of machines and be all but unblockable by court orders to ISPs.