[lolatu54]

I think the only way people would be comfortable is if you use strong one-way encryption, meaning you yourself cannot decrypt a user's data. But to enable trust, and being a startup, you would have to have your code reviewed by a reliable third party or open-sourced for public review. Google gets away with it because they have built a brand with a reputation that some people trust enough with their data (I don't personally, but enough do). A much easier path is to create a version that works locally with no external communication. Both options would be ideal, but perhaps more work than you care to take on. No matter how it pans out it will be a great learning experience.