First, I love the concept. I've often been reading interesting books and wished I could dynamically jump through them. I've even wanted to do this in fiction -- for example, if characters reference something I forgot about, I wish I could just click that and go back to that original chapter/scene and refresh my memory.<p>I suspect that any UI awkwardness will be growing pains caused by it being a new idea for books.<p>Technical Issue<p>1. I click a planet expecting to go to a chapter about that planet (say, Saturn), but nothing happens despite the page reloading and the address bar changing to #saturn. Chrome 43 on OS X 10.10.<p>Content Issues<p>1. I love the animated cover, but it wish it had relatively accurate orbits and periods (within reason). One of the coolest things for me as a kid was realizing that Pluto and Neptune switch places.<p>2. The summary for the book says "all ages," but very shortly in you have a bunch of math and symbols that don't make sense unless you've already had geometry.<p>3. The homepage presents Bubblin as "for developers," which doesn't seem to fit. Do you want authors to present books (as suggested by your own), or do you want developers to use it to present stuff (documentation, use cases, white papers?) about development? It's also at odds with your statement "Meanwhile, to those who are unhappy about the idea of having books with flipping animation on the browser, here's a little tip: A lot of kids, especially my nephews, love it," so I feel like there's a little bit of confusion about the audience. :)<p>A nice idea/platform! I just wish I had something to use it for.