It seems well developed (minus the bugs folks are reporting), but I'm not entirely sure why I would use this instead of a normal document.
The ability to move things around in this format seems somewhat useful, but not particularly useful for any workflow I engage in.
When I create docs for work, I want to tell a story that is quite linear. When I want to tell concepts of hierarchies, I'll make a chart and then paste in the document.
I could see people perhaps storyboarding with this? Creatives?
I would encourage you to find all the types of people who are using this organically and segment the customers, then engage in a vigorous set of interviews on how they'd like to see it improved.
Some of the product decisions, too, seem quite strange. For example, why is commenting something that I have to drag onto the page as well? Why is that not integrated into each box with a click? Or why is that not generic to each board -- 1 chat room per board? These features would ideally be developed with specific customers in mind who say "I want it to work this way!"
This is one of those products that starts off "looking like a toy" but might actually become super useful down the road as it evolves. Good luck!