Recently, it occurred to me that Bitcoin could be used for nearly overhead-free, arbitrarily small payments between clients in a peer-to-peer network. The thing that made BitTorrent succeed where other peer-to-peer filesharing protocols failed was the fact that receivers could pay senders for data chunks they wanted by offering to send them other data chunks in return (“I’ve got A and C, and want B and D; you’ve got B and D, and want A and C; so let’s swap”). This pretty much solved the problem of freeloading that other protocols suffered from.
The way BitTorrent does this is clever: when n receivers want to download a file, the node that seeds the file gives each of them one nth of the file, and tells them to swap chunks among each other until they all have all n chunks. If you want all the chunks of the file, you have to give chunks to the other receivers.
However, the node that seeds the file does so without getting anything in return. And in most peer-to-peer networks (not just filesharing networks), that’s the way it is for all nodes: it works only so long as enough nodes aren’t selfish. But Bitcoin could change that, by enabling nodes to simply charge for services: sending data chunks, storing data chunks (such as for peer-to-peer backup), internet access (your neighbor’s wireless access point), and so on.
Many of these uses would of course be prohibited: your ISP typically doesn’t allow you to resell your bandwidth, and pirating movies is even more illegal if you make money off of it. But that hasn’t stopped peer-to-peer network innovation in the past, and a lot of use cases would be perfectly legal.
One technical challenge is that Bitcoin payments take many minutes to be sufficiently verified, so protocols can’t rely on immediate payments. But that’s just the same situation we have in the real world, with invoices and credit cards (and I hear that they still use cheques in some countries); it involves keeping track of who’s been paying their bills on time in the past, requiring advance payments from people you don’t know, and so on.