Fullscreen mode like Byword/WriteRoom etc.
While the fullscreen mode in Bookle probably works just fine on a tiny MacBook Air screen, it's awful on a large monitor, with a wall of text 16" or more wide.
Bookle should take a leaf out of Byword's book and recognise that fullscreen is more about hiding the distraction of other apps than getting as much text onto the screen as possible.
The text should be ~800px wide, against a subdued background, and the library should be hidden. There's no reason to see the library while you're reading a book, anyway: it's just a distraction. And it's confusing because it looks exactly the same as the TOC (which there's also no reason to permanently display).
Yes, I agree. BBEdit works like this too, and I'd like Bookle to do the same. Lion's full screen mode really is a bit of a blunt object.