steemit.com isn't . but i already have esteem installed... there will be more apps that work through RPC and I personally have a proposal for a combined routing/caching system for eliminating location surveillance of members, which takes it to the next logical step (I am doing a brush-up of my c programming skills so I can do it properly).
Incidentally, this brings up an interesting idea. Hosting steemit could be distributed too. Though the DNS is obviously centralised, even then, there could be the use of a namecoin or similar blockchain name system, that also refers to the multiple hosters.