I love your app, and I have been using if for a while now. The 4th generation is much better in regards to design and the fact that it links seamlessly, through iCloud, with the new iPhone version of the app. However, there a few things missing. First, you should have a continuous scrolling feature; I personally prefer that to page swiping, as I am sure many others do. Secondly, you should be able to lock zoom view while reading; a feature that iAnnotate has, and leads me to, sometimes, use their app instead of yours. Thirdly, you should have the option of having multiple tabs, so that one could quickly swipe through each PDF or notebook, etc. And finally, you should have a mac app as well for those, like me, that love to switch between iDevices and Macs.
For me, these new features would make this app my favorite app of all time, which would most definitely deserve 5 stars.