I think this is fake. It definitely could be faked very easily. It has nearly the same interface as iPhoto. Try opening up the iPhoto .nib files in Interface Builder. You need to open the package to get to them. You can see how easy it is to modify them. The .nib files could be opened up, buttons moved, text changed, etc. One suspicious thing is the area at the bottom, where the text is displayed bigger, presumable scrolling. This is exactly the same as the iPhoto toolbar, except without buttons. The other thing that is suspicous is that Project Builder is open, and Interface Builder is in the dock. If this was seeded to developers, chances are they would not be running project builder at the same time.
The final suspicious thing is the name iBrary. If you think about it, all apple iApps haven't integrated the "i" into the word, iPhoto, iTunes, iCal, iDVD, iMovie. In addition if the word has been trimmed, it has always been from the end, making it much more clearer. The only example so far is iCal, but still.
Besides which, it seems useless. I could see them adding the ability to use pdf files in iPhoto. You can open them I believe, but the text isn't editable and so on. As somebody already said Preview is fine for reading pdfs. Nobody wants to read a novel on the computer screen.