One of the potential use-cases for Ethereum is to create a fully decentralized Git. Git is already decentralized in many respects, but you still need to push/pull with a specific server. If something like Git was implemented on Ethereum you just need to connect to another Ethereum node on the network.
I first became aware of the concept of private blockchains several months ago when I watched a presentation by Preston Byrne of Iris Industries. Vitalik Buterin (inventor of Ethereum) was also presenting in that session, although not about private blockchains. I must admit I was very sceptical of the whole concept. The entire purpose of having a blockchain is so that no one can be prevented from putting a valid transaction on the ledger. With a private blockchain only an agreed list of people can create transactions. The problem, unlike on a public blockchain, is that it is very easy for a majority of participants to get together and prevent another from creating a transaction. The participants and the verifiers are the same people.