Thanks for your comments, we really appreciate getting feedbacks from the community.
How does this differ from other notary services that try to use the blockchain for this purpose ?
At the moment, most of those services only let you do Proof of Existence. Bitproof also provides Proof of Ownership. It means that you will be able to share your file without losing the ownership. Our long term vision is to develop the "Paypal of trust" that will let you make ownership transfers (to begin, you can think about Digital Art, licenses,...). We're also investing a lot in the User Experience, we believe that people should be able to use the power of the blockchain without a PhD.
Not to mention, there is a bias against this type of use (non-financial data in blockchain), how do you plan to combat such criticisms?
A lot of people in the Bitcoin community understand that bitcoin (the money) is only one application on top of the Bitcoin blockchain. Even if OP_RETURN (which lets you put data in the blockchain) disappears from the Bitcoin protocol, there will always be other blockchains willing to accept them. We also think huge technical improvements such as Sidechains or Ethereum will fix all those issues.