I tried to develop an epub reader app for BB10 using their HTML5 webworks toolkit. I know it is probably not the best platform for this given the XML work required for the format, but I couldn't get past the "open a file on the device" step. A quick look through their developer forums showed a lot of people with the same issue.

Oh, and I'm also not experienced with developing apps for any BB platform so I admit that I'm definitely part of the problem.

That being said, I'm rooting for them. The space needs a third player. They really need to figure out simple things like this though.