Not really. All the low-level pieces simply don't exist as usable code yet - yes, you can pay money in a convoluted way (compared to buying almost anything else) to have a piece of data added to a globally distributed ordered list, but it doesn't make a lot of sense to build every piece of interaction on the network on top of that system. "Pay 5 cents to send a tweet!"

You also need a decentralized publish/subscribe system and a useful decentralized search system, both resistant to attacks. The former has some good solutions buried in people's PhDs, the latter not so much. Then you need a lot of UX research and people working on the low-level protocol, high-level domain logic, and the UI.

It'd be a project on the scale of one of the largest open-source projects currently in existence, IMHO.