Hey, this is pretty cool. Just watched your videos. You certainly have a tool which is natural for average person's use, but you may have a barrier in natural use. The page marks is not a natural activity, but scrolling is. So if the system remembers where you are in the document as you scroll while reading, then that's a winner. In addition, a bookmarklet/icon in the browser itself could be better (but you most likely know this already).

In any case, many people have tried creating such a tool. I once used to believe that such functionalities should be part of the browser itself. But there's always been a disconnect between local files and browser. Now in the mobile world, it is even difficult to stay in sync.