Thank you for this beta. 0.6.2 wasn't opening at all on Mac 10.7.5 for me, but this works great.
I like the addition of the separate preview window. I had to go searching for how to turn it on (a menu icon would be nice), but it's really helpful. I noticed that the new preview window and the book view don't seem to handle images at 100% height very well anymore (they stretch to almost 4.5x the window height). The normal book view used to do just fine.