For example, if I install the Chrome extension, and then visit my banking site, are you indexing my bank statements?
Do you only index pages we click Historify on? The answer to that question ought to be in the privacy policy. You're asking us to install an extension and give you access to EVERYTHING we do in the browser, but not explicitly stating the limits on it.
That said, if you're indexing EVERYTHING I browse to, I think this is actually a really killer app. An app with some insane privacy challenges, but a killer one nonetheless. If you're only indexing the stuff I bookmark, that's pretty cool, and a good step forward, but less exciting to me.